Hey sorry to bump such an old topic but i moved from the NGPC to the GP32 and have never looked back.
Currently the major thing is Gigadrive a very good mega drive emu thats got a very high compatability rating (works with most games).
The GP32 has a lot of great puzzle games
Numo
Perfect Fit
Electronia
Puzzle Mix
GP32 games RU
to name but 5 and the last two are loads of diffrent puzzle games in one program.
I would strongly reccomend checking out
www.gp32x.com message boards.
Also a lot of the stuff thats on Zodiac you have to pay for where as a similar think or sometimes even the same thing is free.
The console is worth the asking price for the emus alone
we currently have
Gameboy/colour fully working
GBA about 20% but thats only been in the pipeline for a month or so
Mega Drive at about 80% most games work fully without sound
SNES 80% about 50% of games work with sound
PC Engine 95% Just needs save states and is perfect
C64, Atari, Spectrum i have not tried out but understand they are 100%
Mame has some early games working dont know how good it is.
and most likely some stuff i have forgotten about.
The system also has some very good quality home brew stuff
Beats Of Rage
King Of Fighters
Bokatoid
its a great little hand held