While it's not technically a video game, I would recommend the Homestuck Soundtrack. You probably already have a vague idea of what Homestuck is, as it was pretty prevalent a few years ago and still has a large following if you know where to look. I would also recommend reading the comic, but it's stupid long and kind of hard to get into for most people, so I wouldn't say it's a requirement. The soundtrack was made by Toby Fox, the same guy who made Undertale & its soundtrack. All the albums are available on Sound Cloud; but there are so many that it would cost over $100 if you were to buy all of them, so I recommend only getting a few or just pirating them. Even if neither of those options strike your fancy, they're still definitely worth a listen.
Specific albums I would recommend are Cherubim, Strife, and Symphony Impossible to Play
http://homestuck.bandcamp.com/album/cherubim
http://homestuck.bandcamp.com/album/strife
http://homestuck.bandcamp.com/album/symphony-impossible-to-play
Specific tracks I would recommend are Cascade, The Carnival, and MeGeLoVania.
http://homestuck.bandcamp.com/track/cascade
http://homestuck.bandcamp.com/track/the-carnival
http://homestuck.bandcamp.com/track/megalovania
Other music I would recommend:
Portal 2 soundtrack http://www.thinkwithportals.com/music
Cave Story soundtrack http://www.cavestory.org/download/music.php
Fez Soundtrack http://music.disasterpeace.com/album/fez-ost
Huskybythegeek
Malukah http://www.malukah.com/index.php/music
pLasterbrain
Madoka Magica soundtrack
Avatar The Last Airbender soundtrack
The Legend of Korra soundtrack
Trigun soundtrack
Fulmetal Alchemist soundtrack
Eureka 7 soundtrack