Well I'm back from movie, and post-movie sushi, and post-sushi coffee.
Over all, my verdict is: It's good. Not mind blowing, but it's good. It adheres to the novel very closely with some understandable changes, and a couple of odd by not terrible additions (the JFK thing for instance, not a big deal, but odd).
The script is often ripped straight from the graphic novel, many of the better speeches and moments are word for word (such as the opening from Rorschach, and Osterman's monologue on Mars). I felt slightly underwhelmed but I think it's largely because it's such a close analogue of the comic book I felt overly familiar with it. And after the novelty of seeing them reproduce certain frames from the graphic novel almost exactly in film, then it felt kind of like "ok, now I know exaclty what happens for the next two hours". But that's not really a slight against the film in any way.
They pulled no punches in content. For it's time Watchmen was a very violent graphic novel and they translated that in full. Watching a guy get his arms cut off, not in any way insinuated off screen, but just fully on screen a man gets his arms sawed off by a buzz saw with tons of splashing blood and screaming, it felt a bit like "hostel" at times (a movie I am not in the least fond of). But given the source material and that it's largely just reproducing what was in it, it straddles a very thin line of gratuitous and necessary to the film.
The fights while somewhat stylized, didn't feel over the top matrixy for the most part. Watching Rorschach beat the hell out of FBI agents in a panic still felt very much like he was just a raging maniac that was good at thinking fast, I never felt that it was too over the top stylized to compromise what was in the comic book.
The change of the ending didn't feel at all awkward or forced, and in hindsight seems like a really good idea. Trying to fit the whole island of dr mareau artists/scientists thing would be awkward and bizarre in the context of the film, what they did instead made sense and worked out really well without compromising the actual philosophical content of the ending.
I think for the most part the philosophical themes came through adequately in the movie, though they focused on some aspects over others. It didn't focus over much on the contrast between Rorschach's more deontological views over Ozymandias' more utilitarian views, and the nature of using ideology as a justification for power and authority, but it hit on other notes well. The nihilism vs existentialism came through fine since they just took most of Manhattan's dialogue straight from the comic book. And the ideas of human nature, justice and authority still came through alright. It felt more empty than the novel, but that's just a given seeing as how it has alot less time and space to explore the same material.
Overall as a fan of the novel, I would say it performed adequately. It didn't blow me away like the graphic novel did, but it did a good job of reproducing it. And yes, there is a significant amount of dong in the movie. They didn't stick with the Michelangelo kind of understated penis as with the graphic novel. Manhattan's got the goods, and he's not afraid to show it.
Over all, I really enjoyed it.