He is definitely on a different level. He is like a superstar athlete at the top of his game. I expect Rage to be a hit because of the passion that John Carmack is investing in it.
Sure, you're just running and gunning down a horde of aliens/demons in all of id's games, but doing it is a LOT more fun than in most other games in the genre. A lot of this is actually due to gameplay-via-code and thus attributable pretty directly to Carmack. Turning feels right, movement feels right (not realistic -- right, there's a difference), shooting feels right, jumping feels right. It is amazingly hard to get these micro-gameplay elements to truly feel "right", and few manage to do it as consistently as id has (some other notables here include Nintendo and Bungie).