Perfect Dark is easily the best FPS on the N64, and probably one of the best FPSs of all time!
The single player campaign probably offers the best gameplay of any game ever released. The story takes you through many different environments and utilizes tons of weapons. Fighting aliens, humans, and machines makes this game very different from a lot of the first person shooters out there. The campaign is fairly long, especially for an N64 game. The ability to wander around the Carrington Institute and go to training rooms and a targeting range is a wonderful addition that is unique to Perfect Dark. With the training and target range you can unlock cheats, multiplayer options, and other content. The campaign is challenging even on agent difficulty, when played on special agent or perfect agent, it gets downright hard. Perfect agent is beyond my skill level in the game, and some levels I cannot beat on special agent. The only real complaint about the game is the sometimes laggy framerates due to the limitations of the N64.
With the expansion pack in your N64, the graphics are beautiful. There is still significant drops in the frame rate when lots of explosions are going off or when lots of people are shooting. Sometimes the frame rate will drop just by going into a large open area. This takes away from the game, but not enough to be a tremendous problem. The blood effects, bullet holes, characters, environment...pretty much every graphical aspect of the game is superior to other N64 games.
Multiplayer in Perfect Dark is easily the best aspect of this game. Together with four friends, you can battle it out with each other in many different game modes, or you can team up and fight against bots ranging from terribly easy to bots with beyond-human abilities. The battles can be huge and last for hours without getting boring. During multiplayer it is certain that you will see drops in the frame rate, especially with 4 players and several bots on the screen at the same time. If you have all explosives weapons, it will get choppy almost to the point of not being playable. There are tons of weapons to choose from, and custom lists can be made with you choice of whatever weapons you want. There are also invisibility pick-ups and shields.
Perfect Dark wins in the sound category as well, it has the best sound of any N64 game I have played. The gunshots and explosives roar loudly across the game support for 5.1 speakers. The in-game music is incredible and definitely adds to the game's experience. There is a real rush felt when the music speeds up and you get into a tense situation!
Overall, Perfect Dark is a must have for any FPS fan, of any generation. Even today with the Xbox 360 and games like Gears of War, Call of Duty 3, and the Halo series, Perfect Dark still remains one of the best FPS games ever made. If you have an N64, get this game!