When I think of his defining play, it's either the TD to Witten in OT, or the slide v. MIN where he thought he was putting the game away. Maybe it's weird to think of the slide, since he ended up short, but he did so much on that play that was so smart: tucking it when he had to, the athletic play to even get close to the marker, the obvious decision to stay in bounds, and then the slide not to take a hit. Just smart decisions, with very little time to decide, all around.
And the best thing is, he's got a lot of room to get a lot better. In 2-3 years, he's probably going to be scary-good.