I sell the Retrogen, so you might take my thoughts on it with a grain of salt, or you may believe me when I tell you that the unit is pretty nice.
The screen is incredible, compatibility is pretty good, and the sound isn't so hot.
The sound isn't as bad as you may think though, coming through the units tiny speaker it really doesn't make that much of a difference. Out of all of the ones I've sold; and I've sold a lot of them, no one has told me that they were dissapointed with the purchase.
Personally I've beaten Sonic 2, tried out at least a hundred games or so, played hours and hours of Beggar Prince, and I'm perfectly happy with it.
Street Fighter SCE is very difficult to play on the system. I can do fireballs, but dragon punch and sonic boom motions are pretty much impossible. Mortal Kombat I and II on the other hand I've been able to play with very little trouble. (I can't win "Test your might" challenges, just can't hit the buttons fast enough)
Direct Feed Footage of Retrogen
Crappy built in Firecore games
Here are a couple of videos I put up on YouTube when I first got the system in last week. Thought you might like them.
Oh yeah, I expect that the GEN Mobile will have the same sound and compatible games, but its a HELL of a deal with 20 games built in. THAT is going to be the real hotness. I expect it to be huge this Christmas.