I think it's perfect, with the exception of the joystick... it is a tad too firm for games which require rapid and dextrous joystick movement, and far too easy to do an upper diagonal when you are clearly pushing almost perfectly straight left or right.
Don't really know why people are comparing the build unfavorably to the GP32. All the ports have nice rubber coverings now, the battery cover feels more solid, and I like the new flush screen protector better (so far seems more scratch resistant too). Hell, even the joystick is at least nicer *quality* than the GP32's cheap little plastic doodad, even though it could use some tweaking.
I like the volume buttons too... I remember some people were concerned that a rocker switch couldn't be used as two independent buttons, but since the volume button control is sort've "floating" instead of pivoting on the middle, it looks like pressing both of them at the same time will not be a problem, opening up some possibilities for vertical MAME orientation, etc.