Like James McAvoy said Wondercon, I saw the movie two weeks back and thought it was spectacular. It's changed again from the shooting script as they refine and refine it, but every draft has been closer to the book and about 70% of the movie is now from the graphic novel. In fact, the reason I was there was to tweak little moments here and there to get it even CLOSER to the book.
Also, the changes actually work as there's just no way in Hell analogues of DC and Marvel characters can appear in a big mainstream movie... legally or creatively (since only our fellow geeks would get any of the gags). But the character is word for word identical and the plot, though slightly rearranged, is pretty much identical, the only difference being that the super-villains are now super-powered assassins. The final ending is a bit different from the shooting script, but absolutely bloody brilliant. I don't want to say too much about it right now (it's still too early), but I walked out of that screening and spent an hour on the phone to friends in the UK (despite the fact it was after midnight back home) gushing. I could not be happier about it and Angelina is absolutely brilliant. It's the best role she's ever done.
The big shock for me was how close this was to the source material and even the stuff that wasn't left it open for the sequels. So I'm really, really happy.