One significant trend is seen in his isolated power. It has decreased every year, even adjusted for the league's decrease:
RB League=Iso Above Lg
.310 .163 = .147
.268 .158 = .110
.231 .155 = .076
.197 .149 = .048
Another trend is his speed score took a dip in 2010: career low in 3B (1), SB (14); career high in GDP (17); fielding range down from 2009.
He's young enough to turn it up and have a HOF career. Or it's just as likely that 2009 will end up having been his career year.