Wonderful retro verical arcade shooter NES port.
Sound/Music: There's no music at all in this game except the title screen, which is the same song that plays on several of Nintendo's NES debut games. Sound is basically the same sounds that are in the Arcade version of the game, however just -slightly- improved.
Difficulty: It ranges really. Most of it has to do with your experience. If you're used to this kind of game or have had many past encounters with this game, and most if not all were good, then this should be a piece of cake for ya, until later in the game as the difficulty progresses.
Gameplay: The main idea is the exact same as every other version of Defender or clones you've played; shoot aliens, save people, take warps, and use smartbombs. No huge plot or anything to look forward to in the end, you just play 'til you die.
Controls: Quite simple, however the ship can be a little unresponsive, depending on how much is going on at once. I personally recommend the NES Advantage joystick. It comes in quite handy with this game, and gives you a sense of actually being in the arcade!
Overall: A decent game, good for setting a score and/or passing the time. However, if you let this game frusterate you, I'm afraid you need to get out more. You won't be playing very long due to the fact it's basically endless and you will die eventually, so I'll say this will take you an hour or two before you turn it off. But you'll come back for more at some point.