I'm surprised Expedition to Undermountain (3.5e) hasn't been mentioned yet. It was one of several Expedition to... series of adventure books that came out towards the end of the 3rd Edition era. Each book revisited and reimagined a classic adventure (Castle Ravenloft, Castle Greyhawk, and Demonweb Pits).
I own it, but I've never run it. It's got lots of good stuff in it, but creates a ton of work for the DM.
There's a lot of information in it but it's not very well organised (or not organised in a way I find easy to use, anyway). It wants to provide both Undermountain as a setting, and Undermountain as an adventure and it does a pretty good job of both, but it's hard to tell which parts of the setting are relevant to the adventure itself. If you want to know how important Halaster's Heirs are to the adventure, read all 225 pages and work it out for yourself (that's an example from memory - it might be a bad one!)
I would have liked an adventure summary for the benefit of the DM - obviously the PCs are free to wander around the dungeon as much as they like, but the DM needs to make sure the adventure hooks are in place so the PCs can follow them if they want to.
The adventure element is interesting and quite varied. It's combat-centric, but that's pretty standard for 3.5 edition. The adventure leaves it up to the DM to determine what the realms-shaking event that you're trying to prevent actually is, and the only advice it gives is "if you're stuck for ideas, consider buying Elder Evils".
There aren't any wandering monster tables, just a list of creatures for each level you could use if you wanted to design your own tables. That seemed an odd design choice.
Otherwise, my only slight gripe is that the upper level of the dungeon looks too dangerous for the first level PCs who will be wandering through it. It might work out okay in play (as I say, I haven't run it) but there's lot of EL 3 and EL 4 encounters that could be a real slog - and some of the dungeon denizens are quite happy to ambush a PC party trying to leave the dungeon after being battered by a previous encounter. (And a personal peeve - will the NG inhabitants of the inn really leave the traumatised survivors of such an ambush down there to die if they lack the 1 gp each to pay for passage up? As written, they certainly will.)
The book is also a guide to the Yawning Portal Inn, which is reasonable, but goes into way much more detail than I want or need. This being Faerun, there are probably people who appreciate their favourite characters being name-checked, and maybe folks have fond memories of the irrelevant fest-hall described as being next door, because of some Forgotten Realms novel or other that I haven't read. (And yes, I do know what Ed Greenwood means when he says "fest-hall".)
It also goes out of its way to make the Yawning Portal Inn a place where nothing ever happens. The regulars are determined to protect the family who runs it, and there are a bunch of them there at
all times. The four named chambermaids are
all hard-working and extremely loyal. It's not really the stuff of which adventures are made.
There's a map of the Inn, but it's completely generic. Not only does it not have a 40' wide circular well in the middle of the floor, per the scale of the map there's actually nowhere on the map it would fit.
You can ignore all the excess Yawning Portal stuff, but it's right at the start of the book and there's always the worry that some of this will turn out to be necessary later on. The three patrons who are useful for the adventure (two of them are, anyway - not so sure about the third) get only slightly longer write-ups than Mirt the Moneylender and his wife, who have no role at all. And if you are going to tell me someone is a 5th level cleric then please mention which deity (Lathander, apparently - thanks google).
… thanks for sharing those details!
