Neverwinter Nights: Hordes of the Underdark will include a new 20-hour single player campaign, designed for high-level characters and set amidst the famous city of Waterdeep and the foreboding Underdark from the D&D® game's Forgotten Realms campaign setting. Hordes of the Underdark will significantly expand upon the Neverwinter Nights universe, most notably with the addition of Epic Level gameplay. Based upon the rules published by Wizards of the Coast in the D&D game supplement Epic Level HandbookTM, Epic Levels will be available for characters who have reached level 20, allowing them to advance as far as level 40.

In addition, Neverwinter Nights: Hordes of the Underdark will introduce several new prestige classes, including the Shifter, a druidic class specializing in shape shifting; dozens of new feats, such as Epic Reputation, Craft Weapon and Armor Skin; a multitude of new weapons and spells, many designed solely for epic level characters; challenging new creatures pulled straight out of the Underdark, including Mind Flayers, Beholders and Driders; several new character voice sets for even greater character customization; and 17 new epic soundtracks from composer Jeremy Soule.