I've been giving this a lot of thought. I was so impressed with JJ his rookie year that I thought we had a sure hall-of-famer on our hands. Since then he's teased us with an occasional good game, but never anything to compare with the way he dominated some of his rookie games. I've come to the conclusion that one reason he was so dominant that year was that he had sat out most of the season, and he had very fresh legs to go along with his eagerness to play. His quickness caught everyone off-guard, and he had a level of energy that most defenses just couldn't handle. Since then, on an even playing field, he hasn't been able to dominate like that anymore. I think he's better than many give him credit for, and would look much better if he was allowed to run an entire game and stay in on every down, but probably he won't ever look so inhuman again.
Just my 2 cents worth.