A webgl/browser based 3d dungeon crawler with proceduraly generated levels.
moonpiedumplings
Gameboy roguelike that is simple, but very elegant.
Sadly, since romhacking went down, I don't think it's possible to find the translation patch for it, unless they uploaded it to the internet archive.
A simple but elegant io game. You are a ball, and you want to knock other balls to the ground.
One thing I like is that rounds in small, 4 person lobbies, rather than the massive worlds of other io games. Although you can't really make friends, you can know personas, and it's more personable.
Fork of the older warsow, open source movement shooter. Think quake.
Sadly, it seems to be dead on steam.
A wonderful and life changing experience.
I like to link it without the ending title, like https://store.steampowered.com/app/1944240/ because it's funnier when people can't see the game title in the link.
Learn the pleasures of loving another human, and the pain of being a programmer — at the same time!
A fnaf fangame that is close enough to feel like fnaf, but has a twist: Every single level also involves a puzzle. While trying to survive enemies fnaf style. Although I've never played this game, I LOVE watching it on Twitch. I like to call it "Human's can't multitask: The Game".
Fun arcade bullet hell survivors (think vampire survivors) type game. Dodge bullets, and survive as long as you can.
PhobosLabs
This site has a few high quality browser games. The one I come back to is X Type, a bullet hell shoot-em up that has ever expanding enemy ship sizes, and never ends. It gets hard fast.
I also like Xibalba, which is a Doom/Wolfenstein style game playable in the browser.
The creator also did a rewrite of quake in 13 kb of javascript