Unfortunately, I am not at all sure that a studio will be able to get it on film. I am also not in awe of the 300. It had flare and certainly wasn't a bad representation, but what makes the Watchmen so amazing is its death that slowly builds as the story unfolds. One thinks of Batman, The X-men, Fantastic Four...this comic comments on all of it with characters unique to the graphic novel series, or now the graphic novel, as all parts of the series are in one book.
I would like to think it can be pulled off, but I cannot help thinking there is going to be a loss in depth, and if moviegoers do not get the depth of plot in the original book (which cannot be done on many levels). then it just will not work. It may be a good movie, but fams will understand it more, and forgive what is missing,....or not. Meanwhile, it could detract from the reputation of the graphic novel in general if the audience doesn't understand the relationship these characters have with comic book lore, comic book art, and the characters that frequent the imagination. As usual, I am a pessimist. Good luck to the studio though.