Gonna list 2 that deserve the “great soundtrack” tag on steam:

• Assault Android Cactus - twin stick shooter/bullet hell with cute android girls blasting robots. Techno stuff, with my 2 favorite tracks being Liquorice (it’s divided in 3 “acts” as it’s a boss music) and Assault
• Cloudbuilt - 3D platformer with focus on speed. I suck at this game, but the tracks are amazing, with my fave being Aurora

Someone else mentioned Unreal 1, but I gotta say, Unreal Tournament 2004 has some absolute bangers, like Morpheus3, Hyperblast Redux, Level11 and Convoy