Its called "Perfect" Dark for a reason.
Perfect Dark is set in the dystopia of 2023, where the corporation dataDyne is up to something shady, but it isn't known exactly what, and as the Carrington Institute's best agent, Joanna Dark is sent in to see what's going on, and what starts out as just a few tiffs between the two organizations turns into the continuation on Earth of an intergalactic war that has been going on for years to either protect or destroy humanity.
Perfect Dark plays very similarly to Goldeneye, but takes advantage of the 30 year gap to offer the player a whole new set of futuristic tools. While you'll be given a set of objectives at the beginning to the level as per usual, you'll also be given weaponry that can do all manner of excellent things, such as turning into a laptop, a mounted gun, or shoot through walls. The objectives in each level range from simple rescue and protect jobs, to destroying alien spaceships and uncovering secrets, leading to truly colossal acts throughout the game. Most missions require a degree of stealth from you, and a dose of all guns blazing is required in short bursts. The levels themselves are huge, with multiple missions taking place in the same locale, giving the levels a gigantic feel, which screams to be explored in order to develop the best strategies for dealing with ever changing missions.
Perfect Dark is one of the few games to fully utilize the Expansion Pak in order to boost its visual fidelity. The game runs in a much higher resolution than your average N64 game, but the frame rate does suffer severely from time to time, serving as the game's only real problem. On the other hand, everything from the levels, to the character models to the guns are all intricately detailed, and the enemy goons all animate incredibly realistically.
What further emphasises Perfect Dark's filmic qualities is the use of full, and excellent, voice acting. Accents and tones are executed expertly, and a great script helps to round out the voice work. The mix of techno tunes and atmospheric natural sounds to help make the game feel incredibly realistic.
Before jumping into Perfect Dark, you must be forewarned of one thing: Without an Expansion Pak, you will only be privy to approximately 35% of the game, and none of the single player options. However, those in procession of an Expansion Pak are offered an incredibly deep single player mode, with oodles of replay value due to each difficulty setting offering different and more complicated tasks than previous difficulties. To top off the fantastic set of single player modes, Perfect Dark offers a great number of multiplayer options. You can play the entire game in co-op, go it alone with bots in deathmatch, or bring along 3 friends for a variety of games.
Closing comments: Perfect Dark is the pinnacle of N64 gaming. With a mixture of highly cerebral stealth action along with intense fire fights, and presentational values that border on a film, Perfect Dark truly lives up to its namesake.