I love Requiem for a Dream. I hate Requiem for a Dream. But the Lux Aeterna theme is amazing, whatever you think of the film.
While you can’t really do justice to the piece on a single instrument (especially given the mood you lose going from strings to piano), this guy gives it a good shot. This is from the youtube user Raftaman92. The piano’s bass reverberates in a funny way, but it seems like that helps it to recapture some of the lost intensity of the original. And if you aren’t familiar, the original is rather intense. I love it. It drags you in and commands your attention until several moments after the piece has ended. Give it a listen.