Refunct

Nobody's mentioned this one yet, perhaps because it's a bit obscure, but Vib-Ribbon (PS1) has such a unique and endearing OST. I never played the game, but I heard one of the songs and got totally hooked.

Furi

I love the soundtrack of underdogs. The song i like the most is ready for war (wraz. Remix) by Dominus and magugu. It feels really good in the game when you get in the big boy arena and this song starts.

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

Tecmo secret of the stars.

A Plague Tale is a master work by Olivier Deriviere. Take a listen here. It really amplifies the immersion of the game.

Redout! It's probably the most pulse pounding soundtrack I've ever experienced!

My favorites:

• Superbrothers: Sword & Sworcery LP
• Hyper Light Drifter
• Into the Breach
  • Basically, Ben Prunty does amazing work. FTL and others have already been mentioned

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

Bonelab with would you even know, don't fence me in and turn around. Some of my favourite video game music moments.

I don't think I've seen any shmup OST mentioned, but there's so many that I think are bangers.
A favourite of mine would be DoDonPachi DaiFukkatsu / Resurrection, specifically Black Label Stage 2.

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

Fantastic game soundtracks are the ones which I actually go out of my way to acquire. Chrono Trigger, PixelJunkMonsters Deluxe, SimCity 3000, and Yooka-Laylee and the Impossible Lair.

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