In defend, you must stop waves of enemies from destroying your base, this you do by shooting enemies and buying upgrades, either by yourself or in a group.
There are two modes: a straight forward normal mode with 10 predefined waves of enemies that get harder and harder, which is the best choice for new players or by yourself, and an endless mode, which has endless random waves of random enemies, and can end up being very difficult.
Help file in game, should have no bugs that make greatly affect game-play.
Uses actual NES palette.