Well then, let me enlighten you: "Great" would be throwing for 250-300 yards, with three TDs, and no ints.
He's doing what he's paid to do, at the salary he's earned to do it. He's gotten lucky several times, been very good several times, and hasn't cost us any games by being inept. His knowledge of the playbook and ability to read defenses is probably above average, but his athletic ability is very limited.
He's probably one of the better backups in the league, but that doesn't mean he's been playing great. I'm satisfied with the job he's done, but I don't expect him to carry the team on his back for even a quarter of a game.