I don't entirely agree. Any story can be made shorter or longer: I have absolutely no problem with that. The problem with Watchmen, and in fact, the entire point of the original graphic novel is that it's a story specifically meant to be told as a comic book. Alan Moore uses every visual narrative trick known to man in order to anchor his narrative in the comic book medium. Turning it into a movie annihilates that, and that has nothing to do with the movie's length.
I just re-read Watchmen a few weeks ago, and was amazed at the ingenious way the story was told (at least most of the way). The underlying plot isn't that original, but I really like how it is told (This also means my hopes aren't very high for the movie adaption).
And I guess Rorschach is one of my favourite (anti)heroes.