I'm mildly impressed with what he did at Buffalo (although, it's not like he had built them into an actual solid team, just a less bad team). He's also assembled a pretty strong staff. Truthfully, I wish we had a few of their assistant coaches. Here's how I see things playing out for him and ku.
I think he'll last about 4-5 seasons at ku before getting fired. I don't see ku settling for average to below average with what they're paying him and given the success they had under Mangino. Gill is fortunate to have the soft South schedule right out of the gate. However, the problem for him is that it's during his first two years, when his team will be least able to take advantage of it. Also, his program is behind 3 or 4 (possibly 5, if Hawkins is able to get even a little improvement) Big 12 North teams...and he lost his best playmakers on both sides of the ball. Other North teams will have set pieces in place: Nebraska's strong defense, Missouri's spread offense with Gabbert, K-State with Daniel Thomas and Snyder's coach 'em up skills, Iowa State's got Arnaud and Robinson, and Colorado has the awkward Cody Hawkins / Tyler Hansen quarterback situation. What shape is ku's identity going to take? Kale Pick? Tobin Oporum? Who knows.
Granted, the facilities, talent, etc. at ku is better than it was at Buffalo, but the Big 12 (yes, even the North) is a completely different ballgame than the MAC. I don't see ku beating Nebraska, K-State, or Missouri for at least a couple of years. Gill's biggest challege will be starting off strong, so that he doesn't lose the support ku gained under Mangino (where the easy soft schedule may be a boost). He'll need to beat the Colorados, Iowa States, and Baylors of the conference.
If K-State continues to improve under Snyder and beat ku, that will be a crushing blow to Gill. No matter what ku fans say, K-State is their true rival. I had free tickets to the ku / Nebraska game this year and the fans were cheering pretty loudly about Missouri beating K-State. There was a guy sitting behind me whose girlfriend / wife asked who they should root for, and he said "Missouri" without hesitation.
That brings me to my last point. Turner Gill is going to have to create a football culture among the fans at ku. Even at their most successful under Mangino, that did not happen. At that same ku/NU game, I overheard one young ku fan discussing the price of silver with another young ku fan in the middle of the game. You won't hear crap like that from K-State or Nebraska fans (or other well-supported football teams), no matter how intellectual or interested in the economy they are. There's no reason ku can't have a football and basketball culture. However, if they didn't get there under Mangino, I don't think they will under Gill either.