Dungeon Siege II: Expansion is an action/role-playing game set in a dark, post-apocalyptic fantasy world that concludes the story of Dungeon Siege II. You must hunt down the Dark Wizard in order exact your vengeance and undo the evil brought to the world of Aranna.

• After the shocking betrayal at the end of Dungeon Siege II, play through Act IV to conclude this epic adventure.
• 10 additional hours of primary quest gameplay and an additional 5 hours of optional quests and levels, including two new modes of play, Mercenary and Elite.
• Over 40 new monsters and beasts with powers that will change the way you play.
• New items including all new powerful weapons and armor, as well as enchanting magic items.
• Two brand new character classes that combine the powers of magic and combat. All new spells and powers.
• New pets have been added to enhance gameplay in addition to new races for the world of Aranna – the Dwarves are now back by popular demand!
• All new powers and skills
• New reagent recipes that will allow you to create unique and powerful items.

Official fact sheet from Gas Powered Games.