I liked it, aside from two major complaints.
The action scenes were too damn long. They were infrequent in the book and treated with only a few panels each. It's pretty clear that (in the comic) they were intended to be short, brutal, realistic and have painful and immediate consequences. It was a stark contrast to the violence portrayed in mainstream comic books where, say, Spiderman or whoever gets punched across the city every two panels. The film could have stood out as just as much against recent comic book movies if its fights weren't drawn out into ten minute long Matrix bullet-time spinning kick bullshit with the occasional graphic compound fracture (which, disturbingly, always earned cheers from the people I shared the theater with.) This is a pretty textbook case of what the kids call "missing the fucking point."
Worse, that fault stands out painfully against my second complaint: I don't care if cities are destroyed by blue explosions or a giant vagina squid. If anything, I might actually prefer the way it played out in the film. What pisses me off is that millions of people die, and it gets less screen time and exploration than, say, Night Owl spending a year and a half slow-mo dropkicking inmates while walking down a prison hallway. That squid bluesplosion is the climax of the film, and needs some serious attention to convey the actual gravity and consequence of what happened. Hell, the depiction of the carnage was one of the longest, most inconsiderately brutal parts of the book, and it was absolutely needed. The film gives us a few seconds to look at a hole in the ground, and then we're back to guys knocking each other through walls. It's completely fucking backwards.
I'm heard some of the rationalizations for both of these things, and honestly, I think they're retarded. The way the brutality and violence was handled in the film undercut much of the point of the damn thing.
Hell, it's pretty much stated that the Comedian doesn't put up much of a fight against Veidt in his apartment, yet for some fucking reason we watch those two go at it for what feels like hours. It makes me a lot less sympathetic about any of the rest of what was lost from the film when shit like that should have been the absolute first thing to go. Fuck, it never should have been there in the first place.