Perfect games?

I'm curious what you guys have to say about this. Are there any games you consider perfect? Can a game even be perfect?

My example of a perfect game is always Portal 1. Portal 2 has more going on, but in 1 there just isn't anything to shave off. From start to end, there is nothing I'd change about the game. It's short, infinitely replayable, great pacing. I like Portal 2 a lot in concept, in concept it should be a perfect sequel, but it just doesn't keep the extreme tightness of the original game.