Gameplay
Nightfall is a continuation of the Guild Wars franchise and so follows the same gameplay principles. Guild Wars in previous releases attempted a marriage of Player versus Environment (or "PvE") and Player versus Player (or "PvP") gameplay, starting out with PvP being the logical endgame for the Prophecies campaign, and PvP optionally interspersed throughout Factions play. Nightfall moves away from this as the storyline is more PvE focused than previous campaigns.
Read more about this topic: Guild Wars Nightfall