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.)
Portal’s beauty is in it’s shortness. Perfectly paced, it takes the basic idea, plays with it, twists it, and finishes before it can overstay its welcome. In and out in an afternoon.