Pokémon!!!!!
I've been playing different Pokémon games since I was a kid and up till now I can't get enough of it. I've probably finished Pokémon Ruby, Sapphire, fire red, yellow, leaf green and emerald over 10 times each and I know I'm going to start all over and finish them again in the future.
As soon as I'm able I'm going to get a Nintendo switch and a Nintendo 3DS so I can play the newer and more recent Pokémon games!!!
You should totally get a 3DS; there are some amazing Pokémon games for it. I think a 3DS could be pretty cheap now if you buy it used.