The best game in the Double Dragon series and one of the best NES games, or beat-em-ups for that matter, ever.
Enemy variety and fighting styles keep the game interesting. Theres lots of weapons and they all are fun to use.
What makes this one better than 1 or 3, is the level variety and coolness. One level your throwing guys off skyscrapers, another your trying to knock them out of a flying chopper while not getting sucked out the door yourself.
The game can seem very hard to beat on supreme master at first, but once you are able to master the jumps, its not that bad at all. The last boss fight is very cool too btw. This is one of the funnest NES games ever, definitely worth a purchase if you can find it (hint: ebay)