Of course he wasn't great with EJ Manuel playing quarterback, but when Kyle Orton was playing competent ball the offense got some things going. When Orton lost interest and became more concerned with staying healthy than anything else, the offense regressed.
You need good quarterback play to have success on offense in this league! But then when they do get good quarterback play, we say it's all about the QB and the coach doesn't matter. It's all on the coach...until it actually goes well.