New character traits, such as spells and combat abilities, were welcomed by players, as were the storyline and setting.

The expansion received generally favorable reviews upon its release. The game takes place in two nations of the Forgotten Realms, Rashemen and Thay, which are considered part of Faerûn's 'Unapproachable East'. Mask of the Betrayer continues the story of Neverwinter Nights 2 by following the main character, the Shard-bearer, who is afflicted by a curse that requires the devouring of spirits (and occasionally souls) to survive, and the character's quest to determine the nature of the curse. Like the first game, Mask of the Betrayer is set in the Forgotten Realms campaign setting of the paper and pencil role-playing game Dungeons & Dragons and employs the 3.5 edition rules.

It was released in Autumn 2007 for the PC in North America, Europe, and Australia. It is an expansion pack for Neverwinter Nights 2. Neverwinter Nights 2: Mask of the Betrayer is a role-playing video game developed by Obsidian Entertainment and published by Atari.