Nightfall's first-rate campaign takes place in Elona, an area adjoining the original Guild Wars' play region, Tyria. The player becomes the hero seeking to prevent a mysterious event called Nightfall, which will return an evil godlike being to the world. Of the three Guild Wars games, Nightfall's story is the strongest and most satisfying to finish. The game also introduces Heroes, computer controlled henchmen that can help players on their quests.
As with other Guild Wars games, end-game content revolves around player versus player (PvP) combat. But, unlike many MMOGs, successful PvP play doesn't depend on players having better equipment or character abilities; characters come with the highest level of both these things, so that success relies on skill, strategic thinking and teamwork, and not just on equipment quality.
Nightfall is a MMOG, but only loosely; the only thing that's "massively multiplayer" about it are the towns where players congregate to go on quests or PvP. The actual game areas are "instanced," meaning that individuals and teams get their own copy of the world in which to quest by themselves. This makes the game cheaper to produce and thus free to play, but the trade off is that it prevents potential random encounters with other people. Interaction with the game population happens only in the towns, providing less opportunity to form unplanned "pick-up" groups.