Duke Nukem 64 is a modified port of the PC game. You play the gun toting guy who shoots stuff, Duke Nukem, while you arrive back home on Earth and bring death to the pig-monsters that are causing terror. The game features what is now standard FPS gameplay, allowing you to pick up a variety of guns, bombs & more to destroy enemies while you make your way through the level. There are items that allow you to travel to different areas, such as scuba gear to let you breathe under water, or Vitamin X that makes Duke speed up a bit.
Oh, Multiplayer. You and 3 friends can play split-screen co-op or competitive. If that's not enough, there are even extra tough AI bots called Duke bots. They will ruin you. The graphics are very substandard for the Nintendo 64, but faithful to the PC.