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.)
Chrono Trigger. It’s basically the evolutionary peak of the NES-era console RPG. Every aspect, including the story, art, game mechanics, and music, are best-in-class, with no obvious room for improvement given the technical constraints of the time.