I got my artbook today, so a few details:
It's exactly 80 pages, with no art on the inside of the front or back covers. Front cover is pretty much the same art as on the boxart, back cover has a symbol/emblem in the center (the thing in the logo). As for the art itself, there's a quick bio for each character, along with a few pages of hand-drawn art. For some, there's also an additional 1-2 pages with various anime stills of the character; the rest just have one or two stills along with their bio.
Other than that, each additional character (NPCs? Enemies? Not really sure...), spirits, vehicles, etc get one page each. Following that is around a dozen pages showing most of the in-game models for NPCs & the lead characters.
Overall I'm really pleased with it. I can't compare it to Namco's previous artbooks (as I haven't had the chance to flip through them), but it's really rather well-done,
especially for a freebie. Can't really complain.
Also, if you ordered from GameStop, you really should go and get your artbook ahead of time. I called up mine today, and they only had one left, which I rushed over to snag.

I'm not sure if they put aside some for existing pre-orders or not, but the way they were talking, it sounded like it was on a first-come, first-serve basis. Just a heads up.