Donkey Kong (1994) - not really rare or obscure, but definitely not talked about enough.
It starts out like regular donkey kong but then it goes somewhat differently.
The colorization is only complete with SuperGameboy so it might be tricky to play that way but there is a colorization hack being worked on.
I played the shit out of Donkey Kong Country 2 on my GBC as a kid. A lot of it with that crappy night light attachment that ate batteries and gave me motion sickness playing at night in the car.