I'll still play the genres below but they'll never ne the same.

Recently Clair Obscur E33 has ruined turnbased for me, never the biggest fan outside of tactical stuff like Xcom and Divinity OS series but I enjoyed them when done well like Persona 5 but I'll never be able to finish a Persona game in full now, something I was planning on with P5. I feel like rating Metaphor lower after E33, Metaphor was the best I got for that style of turn based JRPG and now it looks like it doesn't deserve the 8/10. I feel cheated out of 80 hours, which I'll definitely exceed with E33 as I go for a fresh save after the platinum and already at 64 hours.

Divinity OS series ruined CRPGs for me, the are such polished experiences and I know Baldurs Gate 3 will do the same again. Other titles now feel like they are held together by ticky tack and are so non premium compared to the DOS series, the choice feels lesser, the combat, the itemization and just everything else feels inferior now even when the game is really good like Path Finder Wrath of the Righteous, Wastland 3 or Pillars of Eternity 2. They all fall so short and can not get all areas up to scratch unless they completely remove combat like with Disco Elysium and lean fully into the choice and branching paths but limit themselves so gameplay can't ruin it, DE being the best of them next to DOS 1& 2.

Destiny ruined FPS for me, nothing has ever felt the same and not half as good, I still play them but I never feel the satisfaction anymore in vor gunplay even in singleplayer FPS. Cyberpunk is the closest and that's still not close to have as good as Destiny. A VR game called Blood and Truth also had a hand in it. 

Two games on PSVR, Astrobot Rescue mission and Moss ruined platforming for me, the sense of depth is so obviously what gets you killed in those games and after VR it's so easy to see that failure is the games fault and not mine. Astrobot on Ps5 could easily have been a ten if I wasn't aware of how bad 3d games are at creating an accurate sense of depth. I used to love Crash Bandicoot and now I can't even be bothered after the second area of Crash 2 cause the deaths are on the game, not my skills. 

What got ruined for you?

BOTW kinda did that for me with open world games.

After experiencing the sheer freedom and interactivity of its world, playing almost any other open world title just feels so restrictive and static, and I can't help but feel underwhelmed when fire doesn't burn grass, trees can't be cut down, or a knee-high fence or 3m cliff stops my character.

Mario Kart for racing games - be it realistic or cartoonish. None are anywhere near as fun.

Hollow Knight for (modern) metroidvanias. Even the Ori games and Metroid Dread left me wanting to go back to HK.

Ogre Battle 64 - and more recently - Unicorn Overlord for tactical role-playing games.

Eden Ring for Open World games in general. Tho this is probably an unfair standard cause there really isnt anything like Elden Ring in an open world format.

Try Nine Sols, it may change your mind on Metroidvanias. Game is truly remarkable and better than Hollow Knight in a lotta ways. 

I don't know if there are games that totally ruin 100% of a genre, but they do ruin like 95% of a genre (or game aspect), because now my standards are so much higher.

Super Mario Bros 3 ruined most platformers for me.  I loved Pitfall back on the Atari 2600, but now it's unplayable.  I spent countless hours on Mario 1, but it seemed kind of bland after Mario 3.  Almost every 3D platformer feels like total crap to me.  Mario 3 is just too good.  

Final Fantasy 4 (along with FF 6, 7, 9, and 10) have ruined two types of games to me: turn based RPGs and story based games.  I used to love grinding for XP in an RPG.  I can still enjoy some games like this, but they have to be exceptionally good because of Final Fantasy 4 and similar games in the series.  However, I think these games have ruined story based video games for me even more.  I really think 95% of story based video games are boring and I want to skip through the story.  The Final Fantasy games I mentioned have such interesting story and characters, that I have very high standards of what I'll accept from other games.

Final Fantasy 11 has ruined me on most open world games.  To me Bethesda style games feel like a casual MMO.  My favorite MMO that I've tried is FF11, and on top of having a huge world to explore, like a Bethesda game, it also has tons of other players, a robust economy, interesting NPCs and an engaging story.  It blows away single player open world games.  The only other game I like about as well is Final Fantasy 14.  It's hard to say which I like better, because FF14 feels like a casual game that fixed all of the problems with FF11.  So it's kind of better and worse at the same time.  But almost all other open world games feel really shallow and watered down compared to FF11.

None. If I love a game in a genre so much, it makes me want to explore similar or other games in the genre.

Yeah, this. Final Fantasy Tactics and Valkyria Chronicles were amazing, but it didn't stop me from looking at other tactical RPGs.

The closest thing for me would be Mario Kart 8, which is pretty much the only racing game I play these days, but I will look at other racing games. 

Same and then I waste a chunk of money trying to find it and it doesn't hold up. I'm currently trying my best to not buy a JRPG after Clair Obscur cause I know I won't find one that hold up to the standard cemented here and instead I'm just gonna Replay the game on a fresh save file, why try and find another when the best is already in your hands. 

Try a rally game, Dirt Rally (challenging) or Dirt 4 (easier and more fun) and get into the flow of driving slowly at first increasing your speed little by little while listening to your co driver and once you gain confidence to race at speed and start feeling like Neo in the Matrix you'll have fallen in love with racing games again.  

Closest I can come up with were the Batman Arkham games ruining the superhero genre for me. Everything about the Rocksteady trilogy was so well made in every aspect that I have yet to play another superhero game that comes close to the Arkham games. Regardless of what actual genre the game is in, just superhero games in general.