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.)
What I really like is that it is never unfair. Once you understand what has to be done, it is easy to accomplish. So it is a great kind of difficulty. And there is more: The free mod “Portal reloaded” is really great.