One of the other things I liked in this film was the attention to detail. The torn epilet on Rorschach's coat. The eating of the cold beans (missed the sugar cubes tho). Stuff like that.
Yeah there was some small changes, like Ozy replacing Captain Metropolis in the Watchmen meeting where Comedian burns the map. Mason Hollis wasnt killed (or if he was, I missed it with a toilet break.
And there was some stuff that was cut out for time constraints (the news vendor stuff and the news paper journo bits), but keeping the characters in the film was a nice nod to the fan base.
As I said before, I personally dont think changing the "alien" for the Dr. Manhattan destruction was needed, as I dont think it made any more or less sense, but I dont think it hurts the film in the slightest unless you are an absolute 100% purist.
I will say though that I dont consider what comedian did to be rape, as i dont even think he got his dick in before Hooded Justice beat him up!
Oh and as doc said, I absolutely loved the intro montage as it put enough history into the Minute Men without bogging the film down with their backstory! The only way you could have fitted everything in would have been to have made this into a 12 episode tv show or something, but that would have cost the Earth!