My favorite 2D game is Pokemon Lets go Pikachu. Some people like Moonlighter. That's not a bad game either but I can't stand playing Moonlighter as for some reason it's not fun to me. I did see a preview for dead cells and it doesn't look too bad.
Starcraft and Wormax.io seems to be my current favorites as of late. Gotta admit, those worms are fun to kill in both games.
StarCraft, because that was my first major 2d game that I played, that I kept playing regardless of updates. Wormax.io, because of the ease of being able to kill other players worms in.
My favorite 2d game would probably be Slither.io. I love the strategic element behind the video game of working your way up the leaderboard and consuming smaller snakes than yours! It's a quick and easy game to launch when I'm on my lunchbreak at work and don't have time to play a battle royale or time heavy title.
Metroid Fusion. So many secrets, collectables and interesting mechanics. Plus it had a good aesthetic feel with its art and sound. Plus it was challenging without being unfair. I have not played that many 2D game anyway. I do remember the old GTA games and also the 2D flight sims
My favorite 2D game, uh this is a though one as I don't play many, but I guess it is Dionakra, a really really old game I think it came out in 90s it's like a block breaking game with a ball