This ticks all the boxes for me. I love adventures that foreground a specific kind of monster. In this case, it's oozes, and pretty much all the oozes are here.
The location also works for me. The author encourages you to locate downturn in your own setting (which, as someone who runs a homebrew world, I really appreciate), but on the other hand, the town is developed enough that I don't feel like I need to rebuild.
The adventure hook is intriguing, and includes a previous adventuring party who tried (and failed) to clear the dungeon. The survivors of this party are still milling about town as NPCs, and provide ample opportunity for the players to get information through role-playing. It occurs to me that this failed party could also be a teaching tool. If your players are not used to old-school gaming, they could learn a lot from the previous party's mistakes.
And while subterranean ruins full of oozes would be worth the cover price in and of itself, the module's main villain is a more complex and intelligent, with a great backstory and motivation, bringing in the Faceless Lord of Oozes himself. And while the demon lord (rightly) doesn't make a direct appearance, this adventure could easily lead into direct conflict with him later, at a suitably high level of play.
And to add further complications, there are two other factions at work in the dungeon, making it possible for the players to choose sides, gain allies, play groups against each other, or just die fighting a war on three fronts.
Particularly exciting is the optional mechanic for stocking the abandoned library with potentially valuable, powerful, or dangerous books. Left entirely to the DM's option, this section can be used to reward players for through searching, punish them for pointless dallying (some of the books are cursed, and searching provokes Random Encounter rolls), or a little of both.
If this module has a flaw, it's that the maps were created using Dungeonographer, and show the aesthetic limitations of that system. But I use that program myself, so I can't really fault the author there. Also, the bulk of the oozes were taken from Tome of Horrors Complete, and it might have been nice to see some completely original monsters.
Basically, if you love oozes and sewers and diseased rats, this is a short, tight, but well structured module you can easily drop into your existing campaign and even use as a springboard for further encounters with slimes and the demon lord who rules them.ThisThis ticks all the boxes for me. I love adventures that foreground a certain type of monster, in this case, oozes. And this adventure uses pretty much all of them.