I've got one that was minty with the box. It is a solid performer that puts the Atari 2600 to shame, and is not terribly far below the NES in performance. A good comparison (and my yard stick) is to get a copy of Donkey Kong for each (I've also played an original arcade unit).
IIRC I need to give mine a service. ISTR it not powering up last time I tried to run it.
I love how the wall wart is an outlet hider...I swear you could knock a burglar out with it!
I'd imagine in old houses with loose outlets people had trouble with that brick falling out of the wall....Or worse still imagine playing it in a garage or basement and it coming unplugged unplugged from the ceiling...Duck 'n' cover they dropped the bomb lol!