I believe The Beatles: Rock Band came the closest to being perfect. Eveything about that game was just beautifully done and the only things missing was Pro Drums, an option for Keys, and a few more Beatle songs (Hey Jude, Strawberry Fields Forever, Yesterday etc. etc.)
For a game to be perfect I think it’s got to be absolutely pinpoint in achieving what it sets out to do. Doesn’t matter if it’s a small game, or an expansive open world.
I’m gonna go with Superhot. For my money it took an idea, and ran with it to its natural conclusion. It’s laser focused on that one core mechanic and pulls it off so well that I don’t think anyone else has even tried to replicate it.