Patient Gamers

Evil genius has a soundtrack that fits it perfectly. That game has such a good vibe, like playing The Incredibles if they were trying to take over the world

Hi-Fi Rush

Lollipop Chainsaw

Kingdom Hearts

Guitar Hero 3

Tetris Effect for me.

I'm surprised no one said Touhou yet.

https://www.youtube.com/watch?v=XqH79HDfrr8

Also, I see a lot of love for Celeste and Jet Set Radio in the comments. Y'all have good taste.

Rebel Galaxy - country rock genre? Very unique and different sort of music.

Trine 1 & 2 + Transport Fever 1 - instrumental background music good for concentration, working, studying or just relaxing.

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

Citizen Sleeper

I'm surprised at the lack of love for 13 Sentinels - Aegis Rim here. It's a little more on the electronic side but fans of the NieR soundtracks in particular would vibe hard with 13S-AR. A couple of standouts - Lysine and Brat Overflow

The entire Ace Combat series, particularly from 4 onward are almost entirely comprised of the best music I've ever heard. I couldn't reccomend all the specific tracks because i'd probably hit some sort of character limit but each game has a "flagship" track which I'll highlight here:

• Rex Tremendae + Megalith -Agnus Dei-
• The Unsung War (special mention to First Flight)
• Zero
• The Liberation of Gracemeria
• Daredevil

Also will reccomend both the Metal Gear Saga (e.g. ...Metal Gear Saga)

And the Boss themes from Metal Gear Rising

• Rules of Nature
• I'm My Own Master Now
• A Stranger I Remain
• The Stains of Time
• Red Sun
• The Only Thing I Know For Reap
• Collective Consciousness
• It Has To Be This Way

Sonic CD (the Jap/PAL release, not the terrible USA one). Absolute banger.

Sonic 3/Knuckles. Unironically amazing stuff.

Ecco the Dolphin (CD version). Amazing atmospheric stuff. Hard to believe it's the same composer as the North American Sonic CD

Runescape.

Right from the login screen its always been iconic

Bunch of bangers on this list already, but the one that sends shivers up my spine to this day is Crusader Kings 2.

Furi

Civ 3 has my fav soundtrack. My favorite is this gem you get in the modern era:

https://youtu.be/MPe5an9VltI

I just finished Frostpunk recently and have to say I really enjoyed the soundtrack.

One that sicks in my memory years after playing it is the soundtrack for Expeditions: Conquistador.

Marathon 2: Durandal has only one song, the title theme, but I do like it as a good "get one pumped to play the game" song! From the band Power of Seven.

EDIT: Also, while I don't know if I'd want to just listen to it alone outside of the game

never tried

Jets'n'Guns has a soundtrack that works well for the game. Done by the band Machinae Supremacy. One of the game's levels is set in a future Machinae Supremacy concert.

Also, Bandcamp link for the soundtrack: https://machinaesupremacy.bandcamp.com/album/jetsnguns-soundtrack

For me, it's Xenosaga episode 1 on the PS2. It's performed entirely by the London Philharmonic Orchestra and it's my favorite OST of all times