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.)
Both Portal games are perfect. Portal 1 did some much great stuff and portal 2 said fuck it and decided to be more perfect then the first.
I respect this, but always had trouble with portal 2. It has some great parts but is also way too long.