Super Metroid

2D games that don't use L/R buttons are very playable without a controller.

Older systems that didn't have L/R buttons in their controllers seem to work well

Anything from NES, Sega Master System, Sega Genesis/Mega Drive, Gameboy/Gameboy Color and Turbo Grafx 16 tends to work well.

With a controller, the sky is the limit, assuming your phone is powerful enough to emulate the games you want to play.