Honestly it just reminded me of the 2004 debates where Kerry beat Bush's brains in at the first debate. Something about that first debate as an incumbent catches Presidents off guard.
Romney wasn't simply great (although he was), Obama just didn't look like himself. He looked flustered and reactive, when he's always been stoic and sticks to his guns.
Add in the complete tonal change from Romney and it was just a very odd debate.
But it made for a fantastic party.