Super Mario Galaxy has a rather impressive orchestral soundtrack. Composer, violinist, and cosplayer Diwa de Leon makes it even more impressive by performing it all by himself.
I haven't been this impressed by one man performing video game music since Danny Fong's amazing rendition of the Pokemon theme song. Danny only used his voice, however, while Diwa de Leon brings several instruments into the mix, including a violin, a guitar, and the bongos. Which is more impressive, actually playing the instruments or recreating them with your voice?