Movie adaptation of comic - especially ones with many devoted fans like Alan Moore and Dave Gibbons' The Watchmen - is always dicey.
But if the trailer is any indication, The Watchmen movie is bound to be awesome! Always Watching has more info: http://www.alwayswatching.org/news/watchmen-trailer | Large version at Empire
I have no idea if it was the same for V for Vendetta, I will never know what it feels like to see that movie without having read the book. I only know what it feels like to watch a comic book milestone get crushed by the pretension of those dimwits who did Bound and the last two Matrix movies.
Please save comic books. Kill Hollywood. Kill them all.
Then again, in the book Adrian Veidt is presented the peak of physical and mental perfection and in this trailer he looks like "Rubber-nipple-suit-anguished-accountant-man"