He isn't that bad. Most his career he was with the Texans, who were pretty poor, so that can explain a bit of that. Plus, his career QB rating is 74.9 and he has thrown for 14,141 yards. Compare that to Manning, whose rating is 76.1, and thrown 14,623, he stands up pretty well. Factor in, if he was playing regular at the Giants, he would be playing behind the best O line in the league, and would have better receivers/running game than he ever had at Houston, and I don't think we would have to worry too much if Manning was out for the odd game.
He does suck on Madden though.