Just got my GenMobile today. I was surprised at how small it is. It's even smaller than my PSP-2000 (but thicker of course, due to the cart slot). The volume control works fine on mine (and the speaker is
very loud). The music and sound effects sound different than on Sega-made hardware because it's based on emulation or something. The build quality isn't the best. It's not made by Sega so what do you expect. It's very lightweight but doesn't feel like it will break any time soon. I don't really like the dpad. I found it nearly impossible to do a simple Hadoken in Street Fighter II' SCE, and I've been playing SF for over a decade. The cart slot also has an extremely tight grip. I've had to push the system against my stomach and pull the cart out with my whole arm.
Phantasy Star IV works if you start a new game, but you can't load a save file. The screen where you load your save file is all garbled up and it just goes black after you select a file.
I also bought a Retrogen so I'll see how that one is.
Ignore the scratches on the screen. I didn't take the plastic protective film off while taking the picture (Being the idiot that I am, I actually didn't know it was there and thought the screen already came scratched).
I like it so far despite the few drawbacks.