Start with the Conclusion:
The Palace of Unquiet Repose (POUR) is a top-tier adventure, meeting or exceeding all the promises made on its kickstarter - including projected schedule, something that separates those who can from those who wish. I'm not sure what the retail price is giong to be, as of this writing the module isn't for sale on DTRPG. I've paid $20+ for modules that I feel have less value than this module - I plan on shamelessly stealing some aspects of its presentation/formatting that work in ways I've struggled with too much/too little. If you like intriguing NPCs, well-thought encounters, cool magic, monsters that will leave an impression, and ambitious scope - this module is for you. If your players can handle danger, risk, and likely some loss, there is a play experience here I'm confident they will remember long after the last session wraps.
There are some hiccups. To be fair to Merciless Merchants, on their kickstarter update this was acknowledged and patrons were encouraged to submit suggestions for final tweaks until Jan 10. I treat my email like a red-headed step child, and my funded kickstarters with even a magnitude less investment of time and attention, so I did not see this until after the date had past. So any or all of the small issues I note could already be corrected. I'm glad they published rather than endlessly polishing in any case. And to be clear, none of these hiccups sufficiently detract to ding the adventure even a half-star (if I gave star ratings). Everything I don't mention specifically is well-done indeed, and as long as the review is, I don't dive into the specifics of most of the content.
A brief analogy before I get into the meat of the review. As I was reading through the module, the mental comparison popping up over and over was POUR to D&D adventures what Mercyful Fate is to rock music. You, as the DM running a module someone else wrote, are something like a karaoke singer. As you belt out "Living on a Prayer" after two stiff long island iced teas, the point of the evening is to be together making merry; in your exhibition the group is for you, not against you, cheering your effort and contribution to the evening. Very few people, however, ask the DJ to pop on Mercyful Fate before taking the stage - even if a fan of the band few could hit the notes. And those who could nail the performance might still have a stunned audience when the music stopped.
This adventure is loud, fast, intense, unforgiving, and full-flavored; treading the boundary of whether your elfs-and-orcs D&D player might feel exhausted of that flavor by the time they manage to escape and take their leave. It is not languid. It has a singular vision. It is *tight*. It demands the DM has chops, while still doing more than its share of the heavy lifting in bringing about the play experience the author aims to deliver. If you normally call up "Old Time Rock n' Roll" by Bob Seger when its your turn at the mic, you might need to detune this module into your range before session 1. That's neither a slight on the module nor any DM choosing to do so.
On with the review (Warning, numerous minor spoilers ahead)
The first thing a DM should consider is whether they have a city prepared/available similar to Iotha; a vaguely Moroccan-flavored desert trading city, and the module's jumping-off point. While a DM could paper over the getting going without any real depth, it would miss a chance to ease into the tone when POUR gets rolling. Good stand-ins candidates for walking-around detail, if a DMs needs quick and ready-made, are Xambaala from AS&SH, or The City of Vultures from Melan's Echoes From Formalhaut #6. (Until, I suspect, Iotha is detailed in a later accessory from Merciless Merchants.)
Multiple entry hooks each look fun to arrange in play; most of the best set-ups feels like it should be a session in its own right (DM effort required). The rumors will perk interest, and the roster of hireable NPCs give DMs easy platforms for memorable roleplay, many of whom offer concrete advantages to players making the effort to keep them alive in what is to befall them. The standard journey-to-the-adventure-location immediately challenges the PCs with one of the new monster types, requiring them to think beyond "I attack" for success.
Arriving at "X marks the spot", two different means of ingress to the main complex exist. Each path has some of the few areas of the module that didn't seem to quite stick the landing. One path - a secret shaft hidden in a sphinx* recently uncovered from the sands - is deadlier, but also more informative and rewarding. I like how the setup rewards the use of common divination many players neglect. Note to DMs - make sure you use the text description here instead of relying on the map, as this is one area where the mapping symbols available for use didn't exactly match the descriptions. The area is protected by trope-appropriate cave-in, burial, and gas traps, and it rewards with hints and some treasures useful for NPCs or further information gathering. The gas trap is another area where the DM needs to chose between the text and the map - although either choice will work, but the situation shown on the map is deadlier than the situation in the text.
The second path forward is a fissure opened up by earthquake leading to a natural cavern which opens out into the next area. The cavern is a simple lair for a local beast and offers less risk and reward as compared to the other path - but it is easier to find. As a DM I always appreciate not having to blatantly manufacture PC success in finding a way through a single knothole.
Review suggestions for Section II:
I understand working with a limited symbol selection in making the map - it's always a hassle. The risk is a fully-loaded DM misdescribing the scene, requiring verbal backtracking. This might be a case where the fee for a custom symbol is a worthwhile investment, or even a crude amateur sketch (overhead view) ported into the CC3+ mapping style using the menu commands. There are a few other visually misleading map symbols used later in the adventure which this suggestion could also apply to.
The sand trap takes 20 minutes to fill and I'm not clear as to why the players can't just climb the filling sand up to the top? There doesn't seem anything in the room keeping them "on the floor" as the sand creeps up around them. Unless a turn in LL is not 10 minutes? I'm not super-familiar with LL or B/X, or if there are any differences between an turn and an AD&D turn - presume they're the same, because if a turn is a minute than a trapped PC would only have to hold their breath for a minute to survive. My provisional "fix" is adding spigots flooding ichor from the tree in the vitrified garden on to the floor before the sand hits; roll surprise or save (will ponder the preferred math) to notice/avoid.
For the fissure entrance, would suggest an X instead of a black shape NW of area 1. In other maps the black solid is standard for a rock column; it took me a second to realize the NW alcove was the intended entrance point
The statues/doors leading out of the fissure entrance seem off with the rest of the area. Unlike the sphinx area I have no idea why they invested that ritual effort in this otherwise empty natural cave that only opens to the outside world due to natural disaster. As a player I'd waste time searching for unseen context that isn't there to find. I will probably fill this area with the traces of an old supply depot, or something. Or perhaps make the exit to the lake a natural fissure also.
The players exit out into a challenging environment compounded by the first hint of faction play, as the players consider how to cross a toxic lake. A DM can play up the low visibility environment, switching to describing sounds as the players enter the fog (presuming they don't split the party to leave some outside the fog, who'd then risk being picked off by temptation!). Thoughtful players can learn more information here, if inclined to divinations, that my produce light bulb moments later on.
The potential fight or parley with the Sial-Atun is nicely arranged, with sensible tactical advice if players itch for a fight. Note that as written, the hindrance of the fog is not applied to their view-radius since the text describes spotting PCs examining the barge. This feels like an oversight; the DM should move the barge or just simply ignore the risk of discovery there (the players almost certainly will explore their way into view anyway).
"Rising from the lake like some pelagic horror, the necropolis is a replica of Uyu-Yadmogh’s city in life, recast in terracotta and basalt. Doorways are skewed, angles are jagged and rooftops and towers are slanted. Every inch of the city is covered in hieroglyphics and sculpture, layer upon layer upon layer. There is a psychotic beauty to the place, a reflection of the madness of its inhabitants."
This section has a lot of moving parts. 3 different factions run around this area, along with multiple (nasty) guardian monsters; many of whom track and ambush. A DM will want to avoid "ruined urban area" pitfalls here - primarily overwhelmed players blankly stating they start exploring the nearest (empty) house. The setup helps the DM in two ways, here:
1) in two of the three entry points (gates) the first couple of layers of houses are smaller than normal size and it doesn't really make any sense to struggle with them. It's a batshit crazy detail that makes no sense, but works. You as DM will want to steer players from wrestling with this as a Meaningful Detail or mystery to solve, however, because it isn't.
2) Three areas are visible from anywhere - the tower, place, and amphitheater. Use your narration to emphasize these if players don't the hint. I'd probably make the tree and statue visible very quickly if players are anywhere near their vicinity. That leaves one faction's hideout in the ruins, and the otherwise unremarkable building with the secret passage. The latter really depends on how the players handle the tree, so needs no telegraphing; the former may be more of an issue if the players have (otherwise smartly) eschewed exploring generic areas in detail. Just be aware you should breadcrumb trail a way over to the faction hideout; the easiest intel drop comes as an outcome of going to the amphitheater.
One area to highlight for tweaks is the tree. On the chance the players are exploring it as opposed to being led there, the DM will need something resembling the gardens of Versailles. The map is more abstract, and if taken literally shows something akin to the parting of the red sea with a clear path to the tree. So grab a photo of some aristocratic topiary and make a mini-map prior to use. Another area I'd consider before play is how to handle the paranoia of the locals juxtaposed with the peace-enforcing atmosphere of the tree. This is one area where all the details seem to work against each other instead of with. To make all the narrative parts true, I may substitute the insta-calm of the tree with a thematic save vs maze spell for anyone holding hostility in their black hearts.
A last topic for the DM to consider a touch of further investment is in the Nine. You're given more than enough to play them as opponents, but a bit of thought towards the details of why they're teamed up, why the various individuals want the goal sought, and the fracture lines of a likely inevitable infighting, will make the roleplay with this faction smooth. As an example, one of the Nine is a possible hook/recruiter of the PCs back in Iotha. If the DM used that, some prep in how to play out a reunion the players wouldn't expect, is effort well-spent. My initial thought is a different illusionary appearance for her in Iotha, but her distinctive verbal tic a clue the players might use to connect the two after meeting her true self in this damned necropolis. Pair that with some weakness/phobia revealed in Iotha as part of playing out the hook, which the PCs can remember to use against her here, and the seeds of legitimate player pride in good play are laid.
This is the castle proper, and the meat of the adventure. It is an exceptionally well-envisioned pit of rebellious depravity. Your players will have to think. Pigs are well-fed but hogs are slaughtered. Some highlights and points to be aware of:
The artwork for the main entrance is superb. Show that to the players and the tension for how this section plays out will, I expect, be palpable.
In area 9, a bit of map tweaking should be considered so that the # of alcoves match the # coming out of them, since the monsters are described as 1 per alcove. Or just tweak the description to multiple per alcove. This is in no way a big deal, but as DM you might as well avoid the "wait a minute" conversation with the mapper.
Just north of the throne room there's a large circular room showing as filled with debris on the map, that isn't otherwise described in the text (that I noticed). Decide ahead of time if this is impassable or merely a terrain hazard. Your decision will affect what are the best ambush points and escape routes - monsters in the dungeon are either patient or inexorable, and you need to be prepared to play both situations well. Examples of good ambush sites are outside the areas of 6-7, 10, 15-17, 18-19, and perhaps 23.
Bonus points for the sentence clause "...,triple that to an anthropophage or affluent ghoul."
The master of ceremonies is a great encounter; in fact, I'd tweak his communication to telepathic/instinctive, so as to avoid the possibility PCs can't understand him. A memorable combat could erupt here if some patient guardians used this moment for ambush!
The treasure room is everything greedy players hope for, and more. Follow-up adventure seeds abound, and could springboard your campaign for many sessions to come. One item mentioned is a map, and DMs should have a map prepared to hand out (could be as simple as grabbing an interesting map from anywhere online before play, if a DM doesn't dig making treasure maps).
A likely interaction is in #23, with a death mask. The text seems inconclusive as to whether its a single death mask with 3 sides, or 3 separate death masks. Either works, but the DM should pick one to use in narration.
Again, prior to making my main constructive criticism it should be emphasized how well this, the cornerstone area of the adventure *works*. It is a triumph of evocative, sensical, memorable design. PC exploits here will be discussed over leftover pizza for so long as your group endures. So it may seem odd that I would suggest to DMs running it to tone the narration down in some instances. Everything is "vast", "alien", "incomprehensible", "every square inch", etc. The same adjectives going up to "11" are repeatedly used in the module, and 8 times out of 10, that language is absolutely valid. But it does run past the line of mental fatigue in places. If a monstrous statue is vast, and a bed is vast, and a 30'x30' room is also vast...the statue looses some oomph. The art is fantastic, capturing the applicable scenes in ways beyond my expectations - but even the artists declined to truly grasp the secondary detail in the narrations of most of the scenes presented. If the narration often outkicks the artist coverage, it will almost certainly outkick the mental imagery spun up by the players in the heat of the moment while they are dividing their capacity between that and how to deal in real time with the complex, well-conceived environment, and become so much water running off a saturated sponge. The higher you take the players, and the more often, the more necessary it becomes to intersperse some mental parsley so their palette is ready for the next mindfuck.
The piece de la resistance; the big bad; what has defied heaven and hell to its own regrets. The artist outdid themselves and every DM should absolutely print out this piece to pass around the table. The combat (if taken) will be a satisfying conclusion. The repercussions could linger forever. Well done.