He's toward the end, but if he has one more hot streak left in him, he can still have a pretty darn good year or two. He gets as hot, if not hotter, than any Sox player I can remember recently.
It's not as if he's never went from flaming hot to ice cold or vice versa. This could just be one of his weird funks he goes through. He very well could go on a tear and be a MVP type guy by the All Star break. I think he has one more run of that left in him.