Lets see now. Games Romero has worked on...
1.) Commander Keen -series-. The Commander Keen series was id softwares bread when they were starting up. There were six games (I think, wasn't there another? Can't remember now and don't have my copy of MoD around :)), all released as shareware and all successful.
2.) Doom 1 & 2. Need I say more?
3.) Quake. You could argue that Romeros levels weren't the best in Quake, but personally I found his episode to be the most enjoyable.
Stuff which Romero worked on that was a 'disaster' - Daikatana.
One game eh? Woah. You're right we should crucify him! Keelhaul the bastard! Make him pay for that one mistake because he said he's gonna make me his bitch *cries*
Note my sarcasm.
The record speaks for itself.