Interesting that no one mentioned Rebel Galaxy. Granted that the songs are probably not to everyone's liking. https://www.youtube.com/playlist?list=PLRMcXkadosW43B18ZSbYFqBnFn2myQwRw
Patient Gamers
A gaming sub free from the hype and oversaturation of current releases, catering to gamers who wait at least 12 months after release to play a game. Whether it's price, waiting for bugs/issues to be patched, DLC to be released, don't meet the system requirements, or just haven't had the time to keep up with the latest releases.
Rebel Galaxy and its sequel Rebel Galaxy Outlaw let you also customize the soundtrack completely with a very simple folder system.
Undertale, love the Temmie Village song. The OST can be heard in all kinds of videos. Maybe since you liked ULTRAKILL (based on graphics), you'll like Undertale.
NieR:Automata is an absolute banger. It has a banger of a soundtrack and a really great story. I personally love the park area and the forest.
Subnautica, the OST, really helps to create an immersive experience. It is sometimes mysterious, it can be dark but also adventurous. The music kind of guides you through the uncharted lands.
The Legend of Zelda: BotW I know, it's a WIIU/Switch game, and I know TotK is out, but the design and the music of the game are fitting so well together. The OST is so incredible.
Halo 1-3, GTA 3, VC & san Andreas. Tony hawks early games. Final fantasy 7,8 & 9. Tekken 2