Psychedelic games

If you mean flashy games you might try out Super Hexagon :)

I had my best MDMA trip playing Devil Daggers for some reason.

I am not really into this type of games. But I have really enjoyed The Norwood Suite.

Not the kind of games I enjoy... so no favourite from me.
But have a free bump!

Super Mario Bros.

I'd say Hotline Miami has that 70s psychedelic vibe. Definitely Rez Infinite, D4: Dark Dreams Don't Die has some psychedelic elements, Layers of Fear for the horror elements, and I'd lump This Strange Realm of Mine in there also. Haven't played it, but Planetship seems pretty psychedelic also.

Max Payne’s acid level is about as trippy as AAA gets

You should take a look at this:D! Not sure if its a game for everyone but well that game is fun:D!

Have a bump

There's Brainpipe on Steam that looks trippy enough, even though the game itself isn't that awesome.
Otherwise the good old LSD Dream Emulator is always the right choice.

I just eat a few fly agaric, and then go play anything! :D
Totally kidding, totally kidding. Ancient aliens create the best psychedelic games.

View attached image.

You might find Spate interesting for the visual of it

LSD: Dream Emulator (an old PS1 game)

You'll find plenty of that down there: https://steamcommunity.com/groups/TrippyGames

I won The Norwood Suite here and thought it was great, incredibly weird, but great.
There is also Off-Peak, an older (and free) game by the same dev.

Zeno Clash and Zeno Clash 2 immediately come to mind when I think of hallucinogenic mushrooms! :)

Haven't played any psychedelic games so far but thanks for the puzzle and the giveaways

The Void: https://store.steampowered.com/app/37000/
Basement Collection: https://store.steampowered.com/app/214790/ - few meet criteria
Braid: https://store.steampowered.com/app/26800/ nice mindblower
The Bridge: https://store.steampowered.com/app/204240/ - Escher's figure-like puzzle platformer

Dropsy! https://www.youtube.com/watch?v=0l9pVfYsmYE

Tempest 2000
Attack of the Mutant Camels (and it's sequels)
Polybius

And pretty much everything else Jeff Minter has been involved in.

FRACT OSC https://store.steampowered.com/app/243220/FRACT_OSC/

In ultima underworld, you could eat mushrooms and the game colors changed to something really psychedelic.

Yume Nikki. Not really my "foavourte" but first thing that came to my mind. And it gave me some fucked up dreams when I played it for too long.