Flash is gonna die for good in a few days (dec 31st) so I felt this is a good time to ask this question. (Although obviously, there have been large efforts to preserve these when the developers did not. And even then, HTML5 means browser games will continue to exist, even though mobile games have mostly replaced browser games anyway.)

Mine personally were (taking away some of the more well-known ones):

Gravitee 2

Basically a game of celestial golfball. Had a level editor, which was quite fun.

Bonk.io (although this one has a sequel that's not in flash)

Pretty popular for a flash game made in 2016. Basically a game where balls need to "bonk" eachother out of the playing field.

Effing meteors (Definitely one of the games that I probably remember being better than it is.)

Basically a game where you clump up small meteors into bigger meteors to destroy stuff.

Ribbit

A game where a rabbit and frog are fused together and need to bounce like a pogo to the end.

Frost bite

A mountain climbing platforming game.

Sushi cat

A game where you need to eat sushis quickly. Also has cutscenes.

Flash cat

An aesthetic racing game? Not entirely sure.

Chisel

A game where you drill through the planet enough times to move to the next level (man, I had some weird gameplay preferences.)

Dillo hills

A game where you need to time your descents to pick up speed in the hills and fly.

Dino run

An 8 bit game where you as a dinosaur need to outrun extinction.

Raccoon racing

A power-up racing game I remember playing quite a bit. Definitely designed for children, even if that's not very surprising.