I'm going to keep this brief today because I got my 3DS today, and that pretty much took up my whole day. P.O.W.: Prisoners of War is a 1989 beat'em up by SNK for NES. It's a port of an arcade game of the same title, and is the earliest SNK port that I can think of that isn't complete shit. I don't know if they did this one themselves or if Micronics just got better, but I'd put my money on the prior. The music is pretty catchy and the graphics are pretty good.
It's kind of bland for a beat'em up except for the escaping from a P.O.W. camp theme and the ability to use grenades and machine guns. I suck at it and I'll most likely never beat it, but as an SNK fan I felt like I needed to buy it anyway. If you can stand playing any NES beat'em up, then you'll probably like this game.