Of course, commenting on whether or not the movie will be good is premature, but A LOT is apparent just from watching the trailer, not to mention reading the OFFICIAL synopsis from the film, as well as reading interviews with the filmammkers. The bottom line is that this film is very much removed from the source material to the point of being something we've seen before countless times. It'd be a different story if the changes resulted in something that didn't look so damn familiar. But I mean, just from a visual standpoint, there's NOTHING to link this film to the comic. Nothing about it looks like Wanted. As I said on another message board, assuming you were a fan of the comic, but didn't know a film was being made based on the comic, you should be able to watch the trailer with the sound off, and ultimately KNOW, before the title card appears, what comic the film is based on.
Even if you could argue that there are comic films that can stay true to a comic in all ways except the look, we've still got a small line of dialogue in the trailer that kind of betrays the whole concept; Morgan Freeman saying The Fraternity believes in "killing one to save thousands", it sounds like they're making the Fraternity out to be good guys, or at least people who believe their actions are for a greater good. The whole hook of Wanted is that it's villains being evil for the sake of being evil. They fought superheroes and won. How excited can we got for the film, or more appropriately, how are we to help ourselves from prematurely judging the film, when the trailer acknowledges virtually NONE of the source material.