Funny thing about Sega Master System - it's one of those system I would never have bothered with had it not been for the GP32.
For me this exploration of "other" systems has been a great part of the fun of having a GP32.
I would probably never have "discovered" Master System, PC-Engine, Atari ST and to some extend Mega Drive, had it NOT been for the fact that SNES-emulation was not really worth the bother... Funny thing - because those systems actually has so much to offer (I think PC-engine version of Aero Blaster kick Mega Drive butt).
Anyway...
Sega Master System's graphics really impresses me. I believe that if the sound-chip didn't suck so much, there would be no demand for the 16-bit generation
Joking aside:
There a lot of impressive games available for it, but I guess most of them exist in a slightly better version for Mega Drive. However I find the only GREAT Wonderboy game doesn't exist for Mega Drive: Wonderboy in Monsterland.
But I can really only just repeat other people... Howver most of those games mentioned exist for Mega Drive too. Think Psyco Fox is only for SMS though.
Castle Of Illusion, Robocod, Wolfchild is worth checking out.... if just to be impressed by the gfx - compared to what systems like NES and C64 could do.