Why so pessimistic? Let the movie come out first. I think Zack Snyder will do a good job. 300 was very good.
well there's a difference between 300 and watchmen. Frank Miller obviously has an eye for film and he's worked on several movie projects and you can see the big difference between the movie's based on his comics that he worked on (sin city, 300) and the one's that he didn't have anything to do with (daredevil, elektra).
I think that when it comes to Watchmen and DC, creator Alan Moore has been pretty screwed over, and if Synder really cared about keeping true to the legacy of the comic, then he would respect the wishes of it's creator which is to not make it into a movie.
From the look of the previews it looks like it's big on flashy special effects and not so much on plot. I also think that like V for Vendetta, it's a story that captures the spirit of it's time and that trying to change the context to appeal to the modern will lose what it's meant to be.