Plays GBA/MD/NES/SNES/MAME fairly decently as far as I can tell, but performance is not going to be top notch, obviously. Compatibility is identical to the RetroMini with its original fw.
Good:
- really nice screen
- a $25 pricetag
- the shell format is quite nice
Bad:
- not possible to remap buttons, this will make a lot of games unplayable
- mini USB charging port
- no GB/GBC support
Overall, I wouldn't recommend it without cfw, which I hope will be available in the nearish future. Until then, the BittBoy is a much better choice, and not that much more expensive ($35 is possible if you wait for a sale).
With cfw, this will become the recommended entry-level device almost for sure.