What games have you played that have a "perfect fit" soundtrack?

Katamari Damacy
- NAAAAAAAA-NA-NA-NA-NA-NA-NANA-N’NA-NA-NA-NAAAAAA
  
  "BATMAAAN!"

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.
- It's a magnum opus, to be sure. I'll be blown away if Yoko Taro finds a way to top it.
- Genuinely my favourite gaming moment. Nothing before or since from the medium has made me feel as much as that sequence. It's just fantastic. If you game at all you need to try it.

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.
- So uh..... Fun thing about Transistor.
  As the credits roll, Red sings for the first time in the game. The death of her lover at the beginning of the story turns her mute, which is why she only ever hums to the music in the game. During your first play-through. At the end of the game, the credits roll to the tune of "Paper Boats" which is the first song in the game to have lyrics, sung by Red.
  It's an emotional high point that hits hard. She can sing again!
  But there's more.
  In new game+ Red no longer hums during all pause screens. She now sings the previously unheard lyrics of several songs in the game!
  
  I NEVER PLAYED NG+ SO I DID NOT KNOW THAT. WTF LOL😂
  
  Well shit, I guess I have something to do this weekend now
- Bastion's soundtrack still sticks in my head to this day, Darren Korb does amazing work.
  Chants of Sennar has an amazing soundtrack, as does Tunic.

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.
- The artist behind Celeste's soundtrack Lena Raine is really good at that kind of music, her Bandcamp is good for listening

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
- Furi is fantastic. The mechanics are arguably even tighter than the music.
- Totally agree.
  6.24 You're mine
  You are the end
  Wisdom of rage
  A monster
  All synth bangers.
  Introduced me to carpenter brut and toxic avenger

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.
- Also the synthy goodness with those distorted like bass rips or something idk but 👌🏻👌🏻👌🏻😫

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.
- You have no idea how hyped I got as the beginning notes of "Invaders Must Die" played.
  RIP Tango Gameworks.
  
  The closure of tango and the IP in Microsofts hands is a tragedy

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

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.
- Yeah Katana Zero is crazy good, I've had Meat Grinder (Ludowic) on repeat for so long, that song is just perfect in terms of beats to focus to

Diablo 2. The music fit that game perfectly.
- The SFX are pristine, too.
  Also username checks out.

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
- Check out Bomb Rush Cyberfunk, it's a spiritual successor to Jet Set Radio released in 2023. They consulted with Hideki Naganuma on the soundtrack.

Terraria and Stardew Valley
- My day gets 200% better whenever I hear that summer song

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.
- Nier Automata. There aren't even any words in the lyrics, it's amazing.
  Except for the "final" track, "Weight of the World", which is just amazing and chilling, especially in the context of the game and lore if you make it to the end of true ending e. Apparently the Japanese version uses a take where the vocalist started crying during it, and in the English version you can hear the vocalist struggling towards the end.
  And there's the one track that's name escapes me with the robots chanting "become as gods".
  A lot of the other tracks have chanting, but it's intentionally not in any language, despite every track having a pretty heavy emotional feel to it.
  
  The game is magical. Love it.

Castlevania: Symphony of the Night. That game is damn near flawless.
- Castlevania music is a style of its own. Love that stuff.

Diablo 1. I have a hard time playing the game anymore, it's super clunky, but the guitar music from the overworld fucking slaps
- Agreed. The Tristram theme has no business sounding as good as it does. I

Furi
- Came here to say this. Amazing game.

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

I don't see Transistor mentioned. Great moody soundtrack that fits the cyber noir aesthetic wonderfully. We All Become is such a beautiful song.
- Every supergiant game has a wonderful soundtrack. Darren Korb is the composer.

Risk of Rain 2!!!
- so true... most songs build up over the course of the stage (just like the difficulty usually), then when you hit the tp to start the boss it plays an epic boss song
  my only issue with it is that after the tp there's no music, and I often run around after the tp to minmax items, so I have to sit there in silence :(

Doom 2016
Oh. Just actually read the body of your post!
- I mean it's a damn good pick.

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

Vampire: the Masquerade - Bloodlines
- If you like that you might also like vampire the masquerade redemption soundtrack that came out a few years earlier, and the deb of night radio show from bloodlines.

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)
- Nah, that's exactly the type of game that's the right answer.

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
- Definitely Tunic. I listen to that soundtrack to study to

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

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.
- The Battle Hymn of the Republic from Wasteland 3 is amazing

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).

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

ULTRAKILL definitely has a perfectly fitting soundtrack
To quote, "This shit sounds like how coke smells"
- Really make you feel that you are a unstopabble force.

Unreal Tournament. A soundtrack made by the sceners and trackers. If you know, you know.
- And if you don't know, here's a fantastic way to find out.
  
  Ahoy videos are epic!

Both n64 TLoZ and Diablo II are great

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.

Man, just fucking everything by Nobuo Uematsu. Such a GOAT

Breath of the Wild which also does dynamic music that shifts and changes as you play/encounter enemies
- Most modern games do this. It's a little different depending on implementation, but usually there are short loops of music which can transition into one another, and the game attempts to detect what's going on and make smooth transition at the end of each loop into an appropriate new loop based on the situation, so that the music is seamless but still reactive to what's going on. When it's done well, it's basically invisible that anything special is even happening, which I'm sure is irritating if you're the one who had to do the ball-busting labor of getting it all to work.
  Fun fact, LucasArts was already doing this all the way back in 1991, back when video game sound beyond the bleeps and boops stage was still bleeding edge technology. One of a few different ways in which they were ahead of the curve by about 20-30 years if not more.
  
  Like good CGI. The best work is the one you don’t notice.
  Wonder how they did that back then? Shifting the tones up and down?

Demon's Souls. Sparse and somber and sad and like with this vibe of overwhelming (but not overly melodramatic) loss - just like the game (though it's a tad less restrained with the melodrama) haha

Balatro, game has 1 song (with variations), and after 100+ hours I'm still not tired of it.

Tony Hawk Pro skater 2 (but probably many of Birds games)

Literally any of the Ace Combat games! They have absolutely no business going as hard as they do in an arcade-y flight sim but good lord they are just incredible. I listen to the OSTs whilst I’m working all the time when I need pump up music - Zero is particularly good!

I havent seen it mentioned yet, but ultrakill. Holy fuck this game's soundtrack is like cocaine, nothing beats the absolute rush that is every song in this track. From the guitar/percussion in prelude slamming away the drums like your bullets breaking the skulls of whats in your line of sight, to the absolute state of HOLY FUCK the tracks in the p- levels rip into your soul. Its fantastic
- oh yes

First one that comes to mind is wing commander prophecy. Opened my ears to new styles of metal and industrial music I had never heard before then. If I'm limiting to video game composers streets of rage, I still listen to it sometimes.

WarCraft 2

Superhexagon

Stellaris.

Wytchwood has a soundtrack that goes unnecessarily hard. Especially by the docks. Everything about that game is satisfying.

Honestly, The Last Of Us games. Gustavo Santaolalla is a ridiculously talented musician/producer. Apparently, the guy never learned to read music either!

Animal Crossing. Each hour of the day has a different track and it really makes it feel special to play at every different time of day. When your playing and the song switches or makes you want to play more.