Katamari Damacy

Nier Automata

The soundtrack is integral to the experience.

The credits sequence, IMO, is the current high for games as a medium.

When the chorus kicks in on end of yorha, after you ask for help, still gives me goosebumps.

Not normally that kind of person, but the way all aspects of design, music, story, and user input collide make it the most impactful experience I've ever had in a game.

Literally every game by Supergiant. Most recent would be Hades 2, when I finally beat the 3rd boss and start slashing into the fourth area, the music was so hype I was smiling all the way through.
A better pick may be Transistor though. It's kind of a half action half strategy game, where you kind of pause to plan out and execute your next moves. During that pause phase, the music would turn into a muted version, and main character would hum to it in sync.

Also, Journey and Abzu. They simply are experiences that should not be had without good headphones.

FTL and Celeste have basically the perfect soft background music; once you’re played them it is remarkable how many YouTube videos reuse one or the other for their turned-way-down background music

That, and then Grand Poo World 2 has basically the best retro action game soundtrack I have ever heard. I for-real believe that the quality of the soundtrack is like 75% of why it comes across as more polished than any other romhack.

I can't believe nobody's mentioned Furi!

The game is a boss rush fighting game that's incredibly fun to play, and the developers worked with multiple different artists to make the soundtrack. Literally gave them spec sheets for the boss fight they were making music for and info on how the stages progressed etc. So the soundtrack is a living part of the fights themselves. 10/10 highly recommended

Mass Effect, the first one. The soundtrack, being event driven, made the whole thing feel like a space opera you'd watch as a tv series, not just be an RPG.

I know it's cheating since the game is basically a playable soundtrack but "Hi-fi-Rush" brought me immense joy. On of the only games where I was actually vibing at my desk and rocking my head around to the beat.

As spoiled by the picture I chose for the post, my pick is Katana Zero.

Each stage has its own track, and it is not just background noise. Zero carries with him a walkman, and each level begins with him pulling it out at putting his earphones in, then starting the track as the name of the song appears on screen.

Whenever Zero isn't himself listening to something, any music heard is environmental, like the soft background music of a hotel lobby, or the annoying low tones passing through the walls from a party at the neighbors.

If you're a fan, and didn't know, there is an expansion coming to Katana Zero. It's been teased with a few gameplay clips, and a new OST track.

Hollow Knight and Celeste are the two that come to mind for me.

Pretty old now, but Jet Set Radio/Jet Set Radio Future

Cell-shaded skating/graffiti game from my childhood will always have a place in my heart, and my playlists

Diablo 2. The music fit that game perfectly.

Terraria and Stardew Valley

Deus Ex Mankind Divided.
Rain World.
Super Metroid.
I'll second Nier Automata. There aren't even any words in the lyrics, it's amazing.

Castlevania: Symphony of the Night. That game is damn near flawless.

Furi

I don't see Transistor mentioned. Great moody soundtrack that fits the cyber noir aesthetic wonderfully. We All Become is such a beautiful song.

Diablo 1. I have a hard time playing the game anymore, it's super clunky, but the guitar music from the overworld fucking slaps

World of Warcraft vanilla had an amazing score. Still brings chills to my spine. But that might be nostalgia.

Risk of Rain 2!!!

So not quite what you’re asking for, but right when deeprock galactic came out I found this artist on bandcamp called dreamsaboutdogs. They make electronic music, and their album Cursed quickly became my unofficial deeprock soundtrack. It just meshes super well with the gameplay, I dunno.

I told my deeprock homie about it and now he does the same thing, so it’s not just me lmao

Doom 2016

Oh. Just actually read the body of your post!

From the top of my Head:

• Hotline Miami 1&2
• My friend Pedro
• OTXO
• FIGHT KNIGHT
• Savant Ascent Remix

All of those have certified banger OSTs that blend perfectly into the game

For me it will always be the first Dead Space. The sountrack (and sound effects) were beyond chilling.

Is it cheating to say Crypt of the Necrodancer?

Must move to the music's beat, and the music itself is by Danny Baranowsky (other works include the original PCl soundtracks for Super Meat Boy and Binding of Isaac)

Wasteland 3's soundtrack is full of bangers. The ambient music and generic combat music is good, but the game has a lot of special tracks that play over specific combat moments. They are religious or nostalgic songs being covered by modern bands, giving the soundtrack a kind of distorted feel. It's very good.

Early fight.

Alan Wake (the og one). It's music was so in tune with the atmosphere, and it is one of the very few soundtracks I listen to.

Tunic has unique soundtracks for the different areas that totally hit the right emotional chords in each area. And like how getting back to the main hub feels like a relief in every way (sound, colour, brightness, difficulty).

ULTRAKILL definitely has a perfectly fitting soundtrack

To quote, "This shit sounds like how coke smells"

Tunic

Myth II Soulblighter

RimWorld - see the YouTube comments for people telling stories of what each song reminds them of.

Shoutout to 'simple' music that works well in a game - Project Highrise [procedural], Shapez, or Outbound for example.

The original Doom comes to mind for me.