It's not often I agree with Hitler (shown here in brilliantly mashed-up footage from 2004 movie Downfall), but changing the ending really did alter the meaning and significance of the whole dealio. I'm trying to understand why it was done... maybe a giant squid just seemed too silly on film? Or maybe since Watchmen was first written, so many movies have used the idea of an alien menace bringing humanity together (see Independence Day, etc) that the idea has lost some freshness. But a perceived alien threat from the outside has entirely different ramifications than a threat created from within humanity (complicated by the wrinkle that the alien threat secretly is man-made), so it pretty well screws with the whole shape and meaning of the storyline to shift the blame onto Doc Manhattan. I can only imagine that the filmmakers wanted to make a different point, but I think it was the wrong choice. Even apart from wanting things to be Just Like The Book, I simply wanted better storytelling.
I also missed the little thread of scenes between newspaper vendor and the comicbook-reading kid, though the fact that the blast blows up two characters who look like them makes me wonder if their scenes might show up in DVD extras. I wish they had been in the movie, because the ordinary humanity of their scenes, and the beauty of their ending, was something that pulled the original story well down to earth for me. It also gave more emotional punch to their city's destruction, punch which was sorely lacking in the movie -- we see that a city blows up, but we're hardly allowed to care about it before the camera flits back to our heroes arguing up at the North Pole, then cuts to a quasi-happy aftermath. Since the entire first two hours' worth of plot has been built around the horror of this dreadful act, it is a major problem that the act itself is practically skipped over. Those scenes are all out of balance.
It was as though they were saying, "Okay, a city blows up, you've all seen this in movies before, you know how it goes, no need to dwell on the cliche." But it's not real to us unless they give it gravity and emotional truth. And that touches on another problem in translating the book to screen, which is how difficult it is to convey the true Cold War fear of mutual nuclear destruction. I was a kid in the 80s, and even I can barely remember how real it seemed that the US and Russia might blow each other up at any moment. Especially for a younger audience, I don't think you can just present that threat without working to convince us of its seriousness. The comic book came out in 1986, when the threat of an inevitable nuclear war seemed plausible. But here we are two decades later, and in retrospect, the threat seems highly unlikely: we know that neither side dropped the bomb. So if you're going to try and convince me that the threat (even in an alternate-world 80s with Nixon at the helm) is so desperately inevitable that the only way to avoid it is to blow up New York, you're going to have to try a little harder to sell that point.
Still... wow, did this movie get a lot right. The casting was stunningly well done, especially of all the male crimefighters; Laurie was less interesting but okay, and I did like her physical solidity. Seeing her stride/prowl through the prison break scene was the first and last time she really stood out as a powerful presence. Nite Owl, however, was a revelation, note perfect. And Rorschach in the movie was exactly the character from the book, only better. He's heartbreaking with his mask off, and with the mask on, he does some terrifically expressive physical acting. I didn't even recognize Billy Crudup until the credits rolled, but he managed to hit exactly the right mix of depth and remoteness as Dr. Manhattan, carrying the role almost on voice alone. Ozymandias was a bit more fey and flimsy than I'd pictured him, but he had it all going on: the megalomania, the pensive intelligence, the wheels within wheels that you can almost see turning when the Comedian (also perfectly played) sets fire to his superhero plans and introduces him to a whole new level of despair.
I could go on about the visual impact and atmosphere of this film -- it's freaking incredible -- but I'm sure there will be no shortage of people geeking out over this in one direction or another for a while, so I'll leave it at that. In case my criticisms overshadowed my enthusiasm: let me make it clear that I was very impressed with this film. I just wish, in a movie that did so amazingly well by the book in so many ways, they hadn't made that one decision about the ending that undermined so much of the story.