It's tough to get a good read on this book. It almost feels like a few underdark- and dungeon-themed articles and an editionless fluff book got sewn together into a single product. On the up side, the content here is solid. On the downside, it's of questionable value to both players and DMs; there's not enough of value for either to justify the full cover price. I also found it a tad unfocused... The player information is mostly underdark-oriented, rather than dungeon-crawly, as if it escaped from the upcoming Menzoberranzan supplement. [Edit: It appears that it very well might have, because Menzoberranzan is now an "editionless" supplement.]
Anyway, let's start with the good - the player stuff, which is found (mostly) in the front half of the book. As has become the norm, we begin with themes - 7, here, to be precise, in a mix of dungeon-focused and underdark-themed adventurers. Do we really need more themes? Ummm... No, not really. Are they still good to have? Sure! As long as they're good.
And these, fortunately, are good. They are generally fairly potent, mechanically, which is fine by me... Top of the potency list are the Bloodsworn, who get a slightly less-powerful Elven Accuracy at 1st, second-wind-based features at 5th, and initiative at 10th. Deep Delvers are also notable - they make up for some lackluster low-level features with a whammy - Blindsight - at 10th level. Trapsmiths are pretty cool too - they have evocative flavor, and an interesting off-turn Reaction attack which can pick up control effects. There's even a largely out-of-combat theme in the Treasure Hunter, but while their 10th level feature is interesting, it's overall kind of underwhelming. For each theme, there's some good flavor text stating the character's role in dungeons and/or the underdark along with "sample characters" (more fluff text, which I could honestly take or leave). I wish more of the themes used "highest attribute" for their attacks rather than specific stats, but that's more an issue of taste than anything else.
Moving on. I'm on record for basically hating most of the races WotC has come out with since (and including) PHB3, but what do you know? I love all three of the new races presented here! Without them, this would have been a 3-star book at best. Goblins and Kobolds at long last get the full racial write-ups they deserve! And svirfneblin are back!
All three races are given a lot of attention, similar to what was seen in Heroes of the Feywild, but a little deeper. Goblins are mostly in-line with their original MM1 write-up, but presented here with a wealth of fun flavor text, evocative feats (Sneaky Stabber is particularly great), and a full suite of 2-10 Utility Powers. Living Shield looks like fun, but Fast Filch - which lets Goblins pick pockets in combat at will - seems kind of nightmarish to me from a DM's perspective.
So, anyway, Kobolds! Yes, their Shifty power from their original MM1 writeup got nerfed. You knew it would happen. Shifty Maneuver is a pretty good substitute, though, and they can use their Utility 10 to get a twice-encounter Minor Action shift if they're hurting too badly from the loss. Their feats are pretty decent, too; I can see players taking Dragon's Indomitability (roll twice vs. Daze/Stun) and Eldritch Momentum (which is a more direct way for Warlocks to gain combat advantage after moving, rather than relying on Concealment-based feats).
I've loved svirfneblin since AD&D's epic D123 and their original super-overpowered Unearthed Arcana racial write-up, so it's nice to see them here. Yes, they're a marginal race of sorts, but they're one with as deep a pedigree as drow. They are geared more towards Defenders than normal gnomes, and I think one of their feats is probably scheduled for nerfing. (This would be Deep Durability, which lets multi-marking defenders get a theoretically insane number of temporary hit points while using their racial power.) Deepstone Blessing is likewise kind of awesome for Warpriests. Their utility powers are solid, and it warmed my heart to see that one of their Level 10 Utilities lets them summon an earth elemental of sorts. (Ahhh, the memories... That was one of the craziest bits of the AD&D deep gnome. That, and spell resistance.)
So those are the two strongest parts of the book, in my mind, and it takes us all the way to page 52. You might expect classes here, but you'd be mistaken. Instead, WotC tried something new, and the next 20 or so pages are a random grab-bag of class and skill powers - primarily Heroic tier - grouped into loose associations with some organizations the PCs might want to join. I'm ... not really a fan, frankly. On the one hand, it's awesome to finally see new Artificer, Invoker, Battlemind, Psion, Shaman, Seeker, and Runepriest powers. On the other hand, it's scant support (one power! yay?) with kind of miserable organization. Now, granted, with the Character Builder, that's kind of a moot point, but I found the whole chapter rather befuddling. Some of the powers are pretty awesome (Enter the Crucible is a killer L10 Utility, for example, and Timely Dodge is incredible for a skill power at any level) but I'd rather have seen a tighter focus on just a few classes like Rogues and Artificers, or skill powers. I like fluff mixed with my crunch, but the fluff here felt like so much filler.
And that's largely it for the player sections... But, look down a bit. This book has some weird organization.
The next section is long, but I don't have much to say about it. It's generalized information on building and running dungeons, but it's almost more like a field guide or classification system than DMing advice... There's not much here for DMs about building or running the various kinds of dungeons (examples: "Volcano," "Ice Palace," "Death Trap," etc). It more gives a few basic features of each. The next section about dungeon denizens has an equally "mechanics-free filler" feel and provides amazing insights like how people don't much like rust monsters, and that mind flayers are basically big jerks.
That's followed up with Infamous Dungeons, which is a fun walk down memory lane, but pretty useless for actually putting together and running a game. Like I mentioned at the outset, it's like an edition-less fluff book (like the sort of between-editions filler WotC put out in 2007/early 2008) got transplanted into a 4e book and mistaken for DM advice. (With that said, I *liked* this section; I've read through and/or run a good many of these classic adventures. It's just out of place in a game book.)
Seemingly out-of-order, the next (short) section on Dungeoneer's Tools is more player focused, again. My heart was once again warmed to see a 10-foot-pole and ruby lenses on the equipment list. So, the book earned back some of my good will.
Then we're back to more orthodox DM advice (see what I mean about weird organization?) with the next chapter. This has specific, good direction for DMs similar to that found in the Neverwinter book, to help tie the book's themes with potential adventure hooks. It's solid and immediately useful; the kind of DM tips I've started to value. The section on Exploration, Puzzles, Mysteries, etc. is likewise solid DMing advice that's often been overlooked in 4e, to the edition's detriment. There's a good, meaty section following which should help inspiration-starved DMs come up with new ideas for future adventures. This section is 36 pages or so of solid material, but probably not worth the full cover price for DMs who have no interest in the player section.
I don't really know what to think about the Special Rewards section. I get what they're going for, but it's basically single-use, game-breaking Rare items that can be thrown in for exceptional rewards. It's mostly notable for Power Word Kill and Wish, neither of which I'd be very eager to add to my own game.
Not much to say about the next section on Dungeon Companions. Meepo is here, so that's good? I guess? I seem to remember him being a useless mascot sort of character, but he looks effective here. I'd have rather seen Splug get some love!
Appendix 1 is more DMing advice. Appendix 2 is - awesomely - a Random Dungeon Generator! Hooray! I know what I'm doing tomorrow!
So, I'm not exactly disappointed with this book, overall, but I'm not really thrilled either. It has more of an Underdark (as opposed to Dungeon) focus than I was expecting, and the coffee-table-style bits are out of place, but it has some good new stuff to offer. 3-1/2 stars seems fair; I just wish Amazon would let me pick that. So when you see my 4 stars? It's really 3-1/2
(edited for clarity 5/16/12)