I just wrapped up my campaign after about a two year run and can see how people would like it, but have to say that I absolutely hated it. I suspect that what makes it good is that it's a huge self-contained dungeon that contains loads of interesting ideas that a DM could expand into something very impressive.
For myself and my gaming group we thought it was terrible. So much so in fact that we renamed our weekend sessions of playing to the "Weekend of Pain". The editting in the book is pretty awful and there are sections of the dungeon, that while cool in concept, make no sense (Region E, I'm looking at you - I'm not sure why Inevitables and archons would be threatened by Barghests & other wimpy monsters). The other mistake I think the adventure makes is using lots of low-power monsters to challenge higher level groups (Region I -> Gricks do not make a challenge for 7th - 9th level parties, no matter how numerous. Conversely, advancing monsters by doubling thier hit dice is also a bad way to balance an encounter - Region M has an Air Elemental with something like 40 HD). Overall, I think it's probably better used as a series of seperate dungeons.
For the OP, I would recommend the Shackled City hardcover from Paizo. I'm running a second group through it right now and they are loving it so far (or at least I think they are loving it). It's a bit tough (recommended for 6 characters) but I've been running it with 3 player characters who I've allowed to Gestalt and it seems that they are handling it so far without myself having to do too much fudging in their favor.
