i remember 3 popular fangame projects that i really enjoyed:
1. a 2D minecraft fangame called "papercraft". it was basically minecraft, but on a 2D plane. the movement and controls were so eerily similar to minecraft, the camera followed the mouse cursor... it was so impressively coded. i couldn't believe it was a scratch project at first
2. an angry birds fangame called "8-bit angry birds", where you only get 1 shot per level. the original was an incomplete game, and got many remixes adding new content to it; mine was particularly popular. it's my most popular scratch project, to the point where i kinda delisted every other project i made except for it
3. a smash bros. fangame called "super smash bros. ball". it's 1v1 and all the fighters are balls, and you have to knock your opponent by rolling into them with satisfying bouncy ball physics. there are no special moves, so really, what fighter you select doesn't matter, but it was still a really fun time
in fact, i feel like playing these games again right now!