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It's proposed as an adventure for 1-5 level characters, but it's really is three different adventures which could be tied together if you would like. They are connected to the same background story, and possible aftermath, and I recommend to use all of them if your players don't mind a lot of dungeon-crawling gaming sessions.
Thankfully, the book contains much more than the otherwise excellent dungeon-crawling part.
The content
Halls of Undermountain opens with those informations which could be usefull for all 3 adventures, or even if you wrote your own Undermountain story. This includes a short recap on the dungeon's history, a list of possible ways in and out, as well as multiple finely detailed NPC-s the players could meet and interact with. This part in itself could provide inspiration and adventure hooks for multiple different story-lines.
The next several pages deals with storytelling, with the Undermountain as a focus. The authors provide a few ideas to run your own stories, and a random dungeon room generator is also provided. Of course, the later could lead to very strange encounter areas in some cases, but otherwise I guess it could prove useful. The background and adventure hook to tie the three smaller adventures together is also provided here.
Speaking about adventures, while the background (the dungeon) is similar, but the stories still feels distinct from each other. If a Game Master would like to use all tree of them I recommend to do this in the order they are presented, as the later ones feel a little bit bigger threats than the first one. All of the stories feature several interesting locations and/or non-combat encounters you should not miss. On the other hand, many of the combat encounters feels bland, but this is where DM inspiration comes in.
In the first adventure (Zarr's Invincible Army) the players fight mostly goblinoids, kobolds and their crazed leader. In the second (Tombs of Dayan) they face a quickly growing undead menace, while in the third (Scaly Doom) they could even defend Waterdeep itself from a growing lizardfolk army and it's demonic ally. If they solved all three, they may follow a lead to the fate of a missing young noble.
What I feels really a missing opportunity, is that after three adventures of build-up there is no grand revelation - while all lines leads to the missing noble, his fate is entirely left to the Game Master. OK, they provided three different possible ideas for "what happened", but it's only a half page, and I really felt underwhelmed.
After this the book contains even more resources to running a campaign in the Undermountains, including the description of various places of interest, as well as multiple monsters.
Overall I think that Halls of Undermountain is a well-constructed book, with a clear layout and filled with a great quantity and variety of information the Game Master could use. There are really few errors (like one or two traps/effects don't have a DC or other part of their effect defined), but otherwise you get everything to use this stories.
Final words
After reading through the book I have to say I really like Halls of Undermountain, but somehow I also have some mixed feelings. Maybe it's the anti-climatic ending or that some of the fights seems really "flat" (while there are few which is quite memorable), but I feel that this book is not perfect. In the end I give it 4,5/5 points.
Zoltán "Cain" Mészáros
