Keep in mind he just regenerated, and Time Lords generally are a bit strange after they regenerate.
Besides, it's John Simm, and if you haven't seen "Life On Mars" you should, he is a kickass actor.
(this was an especially good episode to watch the Dr Who Confidential of, you get to see a lot of info on why both Derek and John are on the show.)
But anyway, still, a million times awesome. I miss the bug chick, she was one of the best doomed minor characters from the whole new series, imo.