Checked out some PS1 mega collection and randomly stumbled upon this little rhythm game, Vib-Ribbon. Apparently they wanted to let you play it with custom music, so in a stroke of mad genius, the demented fricks made it load and run the whole damn game from RAM. It has very few tracks built in, but they have about as much character as the visuals. Or the character. Ribbon(?) is awesome, and just oozes personality, with wildly different animations depending on your health. It's just really fricking cool.
Bit late to the party, but 10/10, GOTY.