To call this Double Dragon is an insult to anybody that's ever played the arcade game.
The most noticeable thing you'll bear witness to right off the bat is the unfortunate absence of two player co-op--something for which the very name Double Dragon draws its relevance. A two-player option does exist, but it's been downgraded to alternative play, meaning you have to take turns busting heads. How exciting. The story is pretty much the same--right down to the introductory cut scene where Marion is punched in the stomach and taken away by the Shadow Warriors. You assume the role of Billy Lee as he fights to get her back, but you don't have Jimmy Lee (or a friend for that matter) to help you. What you get instead is a completely watered-down shell of the excellent arcade fisticuff that can be had in the original game. Double Dragon Arcade had some issues with hit detection, and the NES makes it far worse, especially when you're fighting Abobos. Furthermore, any weapons you come across are used only for a limited time as opposed to holding on to it for as long as you're able like you could in the arcade game. Most of the goons have made the cut here, especially the Abobos, and a new bad guy has been thrown in the mix--a purple mop-headed kung-fool named Chin.
What's REALLY infuriating is the inclusion of the experience system. Unlike the arcade game, you don't have your full arsenal of attack moves right off the bat--you have to learn them as you defeat enemies. Even more grating, the game doesn't even tell you which new moves you've learned, forcing you to blindly improvise with the joystick. It is possible to get a handle on which move you learn in sequence, but the experience system and complete lack of any direction is simply no excuse. The levels from the arcade game are here to some effect, with the inclusion of some new stages for added "depth". Some stages are designed in a way that make it a chore to navigate, like the new cavern levels with falling stalactites and platforming elements. The platforming stuff is the real cheese here, as they require that you jump across pitfalls and on moving floors, and jumping in itself requires that you press both the punch and kick buttons at the same time. As if hitting bad guys wasn't hard enough.
Although you may not get to play Double Dragon NES cooperatively with your friend, you're given the opportunity to play competitively instead. A versus mode has been added, taking six characters from the game, blowing them up in size (with the exception of the already-big Abobos), and allowing you to have at it in a "no-holds barred" fight. Both players can only fight using the same selected character, meaning you can both play as Abobo, but not Abobo vs. Billy, Linda vs. Roper--none of that is possible. And that's just freaking lame.
As you expect, the graphics and music aren't anywhere near the quality of the arcade version, but I don't fault the NES for that considering the limitations of 8-bit hardware. I do, however, fault the console for butchering a great arcade game and reducing it to such asinine mediocrity. Spending the 600 or so points on this mess is a slap AND spit in the face. Simply put, this game isn't Double Dragon at all--just a sorry excuse for it. Don't waste your money or your time.