I'm apprehensive but hopeful. There are many ways they could mess it up, and I don't really see how they can get the comic book feel of incredible violence and homicidal craziness without having an 18 rating forced on the film, which the studio will not want.
I think the worst thing that could happen to the movie would be attempts to tone it down to be more mainstream or child friendly, and their is a high likelihood that will happen.
However, if the movie does manage to pull off the feel of a Deadpool comic then it will be an instant masterpiece (to nerds anyway, probably no one else.)