When Perfect Dark came out it was by far the best shooter, not one matched it.  It was the awakening of shooters to show everyone how good they could really be.  It's crazy plot about a secret agent trying to stop aliens keeps you in it but all the objectives that you must complete and the crazy gear you get make it by far the best.  The multiplayer in this so far can only be matched maybe by Halo.  This was the first game that let you pretty much get to customize every option of the game.