I have one:
NES is great with VirtuaNES
Master System and Game Gear with Picodrive is great
Genesis is good with Picodrive, Sega CD games with it have slowdown though
SNES is good with Snes9x but some games (usually the troublesome ones like Kirby SuperStar, Star Fox and Yoshi's Island) have slowdown.
Game Boy with GameYob or GnuBoy works fine, some Color games have slowdown or don't emulate a few things (Perfect Dark on GnuBoy runs better than on GameYob but lacks the digitised speech), I think the DS version of GameYob has better performance.
GB Advance with open agb firm works amazingly well
Neo Geo can run using NeoDS, performance is not that good but its playable (beat Metal Slug 2 and X on it)
There's ports of Doom, Duke 3D, Wolfenstein 3D and Quake too, those work fine if you like Prime Hunter's control scheme
Haven't tested for other systems like Atari consoles, Wonderswan, Mame or Neo Geo Pocket.
But like
>>11797991 said, the screen is terrible.