McCown was a decent quarterback during his time in Oakland but he really didn't do anything special. Lane Kiffin liked him because he's a pretty cerebral guy and picked up the offense pretty quick. Decent arm but very little mobility in the pocket, and that gets him in trouble because he has a tendency to lock on to his first read.
He is one of those quarterbacks who HAS to have a running game to take the pressure off. If the game is in his hands, forget it.
That all being said, he's got heart -- something no one else in Oakland does these days. He played through a variety of toe, foot and ankle and hand injuries throughout the year and never complained. Played the role of good soldier when he was replaced by Daunte Culpepper and was one of the true "good guys" in the Raiders locker room, a player who was well-liked by the media and, more importantly, his teammates. Very well respected guy.
Bottom line: I just don't see him being anything better than a mediocre quarterback in the NFL. He couldn't win a starting job in Detroit or Arizona and struggled big time in Oakland when he did get one. Doesn't throw a great deep ball and sometimes will force his passes into coverage.