At the time Street Fighter II' was really impressive, even with the two button limitation. Now you can play Super Turbo on GBA, Alpha 3 on PSP, etc, so the charm has faded...Most of the games with a lot of text are pretty much out of the question since reading it on that system will melt your eyes.
I guess shooters with large bullets would be cool. The first time I played Zonk was on an Express. Hanatakadata would be nice.
I think platformers would be best though. Bonk, Kato and Ken, Blue Blink, Momotaro Katsugeki...Keith Courage...
BTW, modding an Express became a lot easier with that little PCB D-Lite sells.