1. IMO (and I'll spare you my lengthy diatribe about why my opinion is so very valid when it comes to running backs, here), he's easily the best back in the league. Why?
2. God-given stuff: He's 6'3", 225+, has gazelle-like speed (his size and upright style don't make him look as fast as the Titans' guy, but he's close), and terrific body control/balance, especially for his size. Sanders used his freak-like body control better than anyone before or after him, but he was also my size - you simply do not see that kind of grace in a bigger back. Or you didn't until Peterson came along.
3. What separates him from guys like LT is that he's nasty - I don't know if he watched Payton as a kid, but he takes on tacklers like Sweetness used to do - and that's truly rare in top-level NFL back. Most of them will go out of bounds to avoid contact and save themselves for another play - not AD, he wants
every single yard and he'll kill you to get it. The downside to this is that he's exposing himself to more damage that could limit how long he can play, and he's more prone to fumbling because he's working so hard not to come down.
IMO it's the combination of exceptional physical gifts, intense drive, and that nastiness - that's what makes him so good.
Slayton will be coming on for sure and Chris Johnson can be special (
can be - please see Chris Brown for the other possible result), but pound-for-pound Peterson is currently the premier back in the NFL.