I think one of the possible problems with the Watchmen movie is the timing. I think it would have had more impact a year or two ago, when we were still in the grips of the Bush administration.
When the movie "V for Vendetta" climaxed with the explosion of the British House of Commons, I turned to my wife and said: "This isn't a movie-- it's a call to arms".
I don't have a problem watching a movie made from a book. I don't compare the two anymore, just accept it as the same story told through two different media. I think "Moby Dick" taught me that. I love the two movie versions of it even though a movie doesn't stand a hope in hell in capturing the book, verbatim. But I loved the book, too.