Double Dragon II was near the pinnacle of 2D side-scrolling fighters for the Nintendo.
You play as one of the brothers Billy or Jimmy Lee. The game opens with your girlfriend being shot to death. The man responsible is the mysterious "Shadow Warrior". You are out for revenge, and your brother may or may not decide to help if you have a friend to play with. You quest for revenge involves a lot of basic punching and kicking. As a sequel, DDII cleans up the graphics, improves the fighting system, and adds the game's signatures technique, the "Whirlwind Kick". Ryu and Ken would later adopt the move in Street Fighter II and sequels, known as the Tatsumaki Senpuukyaku. In DDII you will also have access to the myriad weapons dropped by your felled opponents, such as shovels, morning stars, and grenades.
Double Dragon II does not exactly break the mold. You progress through each of four stages before facing a boss character. Between stages there are short cutscenes that feature text and still images that update you on the story. However, the game is basically a punch, kick, and timing game of survival, so the story is more ancillary than central to DDII.
Graphics: For the Nintendo, the graphics were good. There was little of the "flashing" that occurred when there were too many enemies on screen nor slowdown. Characters looked good and moved well, and each stage felt unique. Overall the graphics were pleasant, but not as good as, say, Ninja Gaiden.
Sound: The sound effects were typical of the NES, with appropriate slashing and thumping noises depending on the attack used. The music was suitably intense without becoming annoying.
Gameplay: The game was a standard 2D side-scrolling fighter. It took the formula, allowed you to pick up enemy weapons and perform a spin-kick. At the time it was extremely entertaining. Today there are better alternatives, and games like TMNT: The Arcade Game and Turtles Through time had more varied gameplay and better controls, but DDII gets points for nostalgia and good execution.
If you have never played the Double Dragon series you will be mildly entertained for some time. A better alternative is the underrated River City Ransom for 2D fighters. The basic gameplay has appeal for hard-core gamers. The game really shines when there are two of you, because the teamwork can make it infinitely more fun. Old-school gamers will immediately recognize a classic of the NES era, and will likely be sucked in for an hour or two, themselves.