For a 2d platformer I've gotten a whole lot of mileage out of Celeste. I'm 3000 hours deep into this game and with it I've done a little speedrunning, a whole lot of playing mods, just as much making mods, a heap of deathless challenges and even some TASing! Celeste has a super friendly community and I've met some of my favorite people through it. Check out all these links to my several Celeste things!
SiIvaGunner is a youtube channel that uploads bait and switch video game music. Like you think youre about to listen to your favorite retro game's title theme but some asshole swapped the melody so it's the Flintstones theme. But the thing is, once you're in on the joke, it just becomes a really good remix channel? The people running it can be super creative and despite uploading multiple times a day every day since 2016, SiIva has always kept things interesting.
If you're familiar with Homestuck already I'm sure you're already clicking off the page but I think it's cool!! Nothing tickles my brain like a big overconvoluted mess and if that isn't the perfect descriptor of Homestuck I'll be here all day trying to think of one. I love the diversity of rules and what I guess you'd call game mechanics if they weren't in a non playable webcomic, it all tickles the imagination for me. Not to mention the stellar character writing. I am literally John Egbert in real life, you guys. It's so real, I swear. Trust me.