It's called acting
I don't understand why most people are complaining about Sean going full-fledge; isn't that the whole point of acting, to become another person? He did a great job protraying the character without being to offensive, which a lot of people can't do.
Anyways, this was a great movie. I saw this on On Demand and it was a really good movie. The only thing that pissed me off was TNT, who sponsored the movie, put commercials for their television shows every 5 minutes in the movie.