A bunch of us got in to the Pacific Science Center's "Science with a Twist" cocktails and pre-release screening of IMAX Watchmen last evening.
I think that people who have not read the comics and are expecting a "superhero" movie will be disappointed. This movie, much like the comics upon which it is quite faithfully based, is social commentary with superheroes as metaphors. Those expecting a dark, gritty take on an alternate history version of the cold war with a bit of murder mystery thrown in will enjoy it as much as I did.
It was a long movie, with few action scenes. But because I wasn't expecting "Ironman" this didn't bother me. I thought the portrayals of the Comedian and Rorshach were spot-on, really amazingly so. I was disappointed that Nite Owl wasn't all pudgy and middle-aged, but that probably would have made the few actions sequences the movie DID have even less believable :)
The ending is different. I actually had the specific changes to it spoiled for me, and even so thought it made perfect sense. Having seen the movie, I can say with even greater certainty that they were quite faithful in adapting the ending, they just changed some of the details, and for the better. I highly doubt the movie audience would have "bought" the original comic ending, at least not without adding another hour to the movie's length to seed the lead-up.
I enjoyed the nods to the comic, the newspaper vendor and the young comic-reading kid on the NY streetcorner, which are fairly significant minor characters in the comics, get some silent screen time. I agree with montykins
that the dialogue between Silk Spectre and Dr. Manhattan on Mars was merely "good" whereas it was one of my favorite scenes from the original comic. They cut it short for completely explicable movie reasons, but still, that scene in the books really highlights just how "alien" Dr. Manhattan has become, and that Spectre's attempts to persuade him are doomed to fail because of a sheer lack of common reference. That makes her eventual, almost accidental success even more interesting.
One minor gripe: We didn't need Bubastis. It was a needlessly distracting bit of cgi that didn't add anything. Yes, in the comic Ozymandias has a genetically-engineered pet cat-lion-thing. In the movie it was a bit of random weirdness that just shows up, distracts us visually from the story, and disappears again. Unnecessary.
Overall, though, I thought this was a really successful adaptation of the comics, and Jane informs me that it was a perfectly explicable movie even for someone who has never read the source material.
Oh, and for the players in my old Section 2 game, Ming made a pretty good Ozymandias eh? :)