Mine is Lady Sia for GBA. It's just a platformer but I just love it played and completed more 20 times. Will probably speedrun it in future.
I loved playing a game called Zeliard when I was a kid. I never hear it talked about, but think it could be pretty fun even today for people willing to tolerate 30 year old PC platformers.
I haven’t played it in a long time, though, so maybe I’m forgetting some terrible aspect of it. Should try and dig that up...