Improvements on the GoldenEye engine included the ability to have two separate "modes" on weapons, and the ability to jump off ledges. These improvements required more processing power however, and the N64 RAM Expansion Pak was required for many features of the game to be accessible (including the 1 player mode).
A 2D Game Boy Color game of the same name was also released in the same quarter as the N64 version. The two games could share data by utilizing the N64 Game Boy transfer-pak.
Rare has announced that they will be releasing a sequel, Perfect Dark Zero, for the XBox.