The movie is a solid B+. Frankly I felt like it was in the A range until the last 20 minutes which struck me as rushed and pointlessly unfaithful to the source material. That is, the "new" ending did not seem any less convoluted than the comic ending, while the stated goal of the filmmakers in changing the ending was to make it more easily comprehensible to movie audiences. The conclusion also lost a few points for rushing things ("Hold on, let me explain these crucial plot points while I'm punching you; the money people say this has to come in under 180 minutes"). The film started out at a great, leisurely pace which gave the characters time to interact whereas the conclusion was a trainwreck. The first cut of the film was supposedly close to five hours, and I can understand why. Personally I'd gladly have sat in the theater for an additional hour to see the climactic conspiracy developed more completely.
I have no idea who any of those actors are (I neither watch TV nor get out much in terms of movies these days) but I think they were all magnificent with the exception of Ozymandias, who seemed like a high school play actor following instructions far too literally ("Act…pretentious now. Furrow your brow.") Perhaps that is also a function of the fact that the film devoted almost no time at all to developing Veidt's personality, narcissism, and ambitions. If anything, this was the big flaw with the film. With copious amounts of screen time devoted to Rorschach, Dreiberg, Comedian, and a suprisingly good Silk Spectre, Ozymandias (and to a lesser extent Dr. Manhattan) was short-changed.
Although I have never said this about a film before and meant it, I am looking forward to a full-length uncut/director's edition of Watchmen on DVD. I understand that the casual moviegoer wouldn't put up with a film any longer than the theatrical cut, hopefully the option of a longer film will be made available to those who want it.