Nice to get some fresh legs in the backfield, but unless that o-line is greatly improved (which I think they almost fixed it) you can put any rb back there you want and they are going nowhere.
Sure Shaun sat down a few times, but game after game the defense would pour through that o-line as he took the handoff.
Barry Sanders is about the only rb I can think of that could make runs happen with absolutely no blocking support. Shaun is no Barry Sanders.
The running game will improve this year - not so much because of who is running the ball, but because of the improvements made to the o-line and possibly because they got a new 0-line coach.
my .02