Personally, mine is rocket league it's just the continuous practice that you do. Its not a try hard game, and you see yourself progress from a noob to a decent player. It takes a while to master the perfect airiel hits etc.
there is also a pretty decent trading system aswell. I can hook you up with some good shit if needed.
Aim prac & DM's on CS. Easy to hit 1-2k kills and not even realize when you are in meta ts with friends. Surf server and other mini games are also awesome at times
Overwatch (personally I find it fun especially if you've got a team to play with but not everyone's cup of tea), Cities Skyline is quite good if you like them kinda games
Undertale
OneShot
Darkest Dungeon
Nuclear Throne
Kerbal Space Program
Trackmania Nations Forever (free)
Prison Architect
Bastion
VA-11 HALL-A
DDLC (lol hf)
The Long Dark
Binding of Isaac Afterbirth + or whatever the fuck it calls itself now
Stardew Valley