Of course he's not the greatest RB ever - Payton is, followed VERY closely by Sanders, Brown, and many others. He doesn't have the body of work to be even jokingly considered with that group yet. He sure as hell has the potential to be, though.
BUT: Sweetness fumbled, y'all - I grew up in Rockford, IL and I watched his every move like a hawk, because he was (and still is) my hero. He fumbled, and much of the time he fumbled trying to do a little too much, just like Peterson does. Another all-time great, Gayle Sayers, put the ball on the ground a little bit, himself. Any player, given enough touches, will commit turnovers - strangely enough, QBs seem to get more of a "oh, shucks - that's just how it goes" treatment than RBs do.
I'm tempted to think that the Vikes have botched it with this kid - at least this year. One, they went along with his foolhardy weight gain plan, and that's taken a gear off his speed - not a big one, but this year he's getting caught where he would previously outrun everyone. Two, his fumbles have been so harped on that you have to think it's in his head now, and that's the worst possible result - you think too much out there and you're dead.
Still, if you folks in Minnesota don't want to deal with the fumbles, I know a team that'd happily take this "problem" off your hands.