Exhumed (Powerslave) on Ps1 and Saturn would be a good choice, unforgettable and very creative yet extremelly ignored game.
Also I loved The Adventure of Lomax for Ps1 but feels like nobody played it
Little King Story on Wii was extremelly fun it definitely deserved better sales
Drill Dozer and Alien Hominid for the GBA were a blast
I'm now playing Jeanne D'arc on PSP and while I still early on the game, definitely feels like it deserved way better sales.
Oh and Kirby Rainbow Curse for WiiU was massively underrated