I've been impressed by McCown in his three starts, all of which I saw on DirecTV. He's big, can scramble, has a strong arm, and for the most part has avoided the kind of mistakes that inexperienced quarterbacks usually make, like throwing into double coverage and making bad throws that are easy interceptions.
Today was his weakest game of the three. And, still, what did he wind up with - something like 22 of 33 for over 200 yards, with 2 TDs and 1 interception? That's not too bad against a team that was playing for a playoff berth.
And the TV guys said his quarterback rating in his first two starts was over 90. If you get a QB consistently around 90, you've got a winner.
Give him some experience and a little better supporting cast, including a more imaginative offensive coordinator, and he will be a good NFL quarterback.