It's good, but I haven't used it much so far -- it's VERY large, and even just reading the general information and a single district of town (like I am for running the Legacy of the Ripper adventure from Goodman Games) is a lot of reading to do.
The adventure concepts are most detailed at the lowest level, and include mixing it up with rogues, going underground against some low level baddies (ratmen are the ubiquitious low level monsters beneath Ptolus) and eventually getting pointed towards the Chaos Cults.
Fully detailed locations include a large complex lair of fiends in the city's Necropolis section, two different evil overlord's theoretically disused citadels, a large portion of a ruined dwarven city, a tower that can only be seen in the city by its shadow and a few others.
Most of the adventures take place on the city streets, below the streets or along the spire. I'd say the bulk of the material is intended to pit player characters against the Cults of Chaos, with sidetrips over to the Night of Dissolution module and/or the Banewarrens (Monte actually has some suggestions on making those two one giant module, including which chapters to run when) and then eventually to the two overlords' lairs (although they're MUCH higher level than the lower stuff) and, in theory, even to one of the moons one day, although I don't think that's required to wrap up the NoD storyline at level 20ish.
There are a fair number of prestige classes, although the three for the local wizards' guild aren't three full PrCs: They're each one level and have differing prerequisites. The good news is that a higher ranking PrC level can be substituted for a lower level one, once the requirements are met. (High levels able to be cast, more years as a member of the Inverted Pyramid.) There's also a villainous PrC, a knight PrC for bards (reprinted from the Book of Eldritch Might I) and a knight PrC that can pick a different saint to venerate each day, with varying abilities (which I believe is reprinted from the Book of Hallowed Might).
There are a good number of spells, including one that lets arcane casters access a secret 13th month of the year. (Which is both as awesome as it sounds and much more complicated for the caster than merely getting a chance to catch up on some of their reading.)
There are only a handful of magic items, all of them pretty closely tied to the setting. There are new magical weapon qualities for firearms, since those are a part of the setting.
There's a fair number of monsters, although I definitely recommend buying a hard copy of the 3.5 Chaositech book, since you'll want the ones from there as well, if you follow the Cults of Chaos storyline.
If you're a DM who makes up their own adventures (and maybe owns some of Green Ronin's Thieves World books), there's enough here to run a very long campaign dealing with street criminals as well.
I'd say the adventure styles supported by the book are as follows, from the most-supported to the most lightly supported (but still with ample material to do so):
1) Cult-smashing/world-saving adventure path that includes the Night of Dissolution and/or Banewarrens.
2) Delver's Guild/Delver's Square: Dungeon-crawling adventures beneath the city (optionally including the not-included Queen of Lies or Monte's Atlas Games modules, except for the dragon one, which I think is set in a town north of Ptolus).
3) Street thugs, either as a member of a gang or guild or as a member of law enforcement. (The Vigilante and Streetfighter PrCs from Complete Adventurer read like perfect fits for this.)
4) Intrigue among the noble houses and the various competing political factions of the empire (including the Church of Lothian).
5) Wacky Discworld wizardly adventures on Dweomer Street (optionally including the Pointy Hat tavern write-up from the Delver's Guild), although maybe that's just me. A more serious version of this would also include intrigue with the Inverted Pyramid wizards guild (whose pyramid is fully detailed and the guild is also well-detailed with special magic items) and the mysterious Iron Mage. Probably would go well with a dungeon-crawling game.
