The theories abound...Is he a one trick pony?
Apparently he's been working on another pitch or two for fear that the league "has the book" on him. Felger, on WEEI, surmised that his experimenting around with a new pitch is why his walks are up so much.
I still see him as a fastball kinda guy. I haven't seen him throw much else, but I haven't seen every game.
Regardless, I think he's fine between the temples and that's most of the battle for a closer.