The player controlled protagonist finds themselves changing alliances once their friend, Drevin, is killed in the main story line and works to defeat the villain Valdis.

Developer Gas Powered Games improved the old system into a more versatile one that incorporates additional elements of strategy.

By default, the new system turns off much of the original game's combat automation and requires players to click once for each individual attack of their selected character.

In the original Dungeon Siege, the four character specialties (also known as classes) differed only in the items and spells they were allowed to use.

For example, melee-oriented characters can get better at using a shield to defend their allies or they can improve their two-handed weapon skills to more effectively attack opponents.

A character learning skills in too many different areas may find themselves spread too thin and unable to perform any role effectively.

For example, the Fist of Stone is able to cause small earthquakes when attacking to keep up with the damage output of a pure melee character, and the Blood Assassin is able to cause targets to hemorrhage blood to keep up with the damage output of a pure ranged character (as they multi-class, they cannot upgrade their weaponry as often and would otherwise be weaker in combat).

Emanations are special pet-only auras that provide beneficial effects to friendly characters within range (such as increased mana regeneration).

Weapon enhancement spells, used by the Fist of Stone and Blood Assassin characters introduced in the expansion, also do not count towards this limit.

The party must then find a way to retrieve its fallen equipment, either by venturing back to the characters' corpses or by having them summoned to town by a Necromancer NPC for a monetary charge.

Dungeon Siege II supports multiplayer cooperative gaming over LAN, the Internet, and the GameSpy network.

The GameSpy environment limits the amount of online cheating that can take place, but as of late beta, the possibility still existed.

GS network makes an attempt to support only original games; unlicensed copies are blocked if they cannot mimic the CD-Key.

[4] The game begins with the player-controlled protagonist and their friend, Drevin, serving as mercenaries in the army of Valdis, a warlord who has aligned himself with a race of Dark Wizards and wields the magical Sword of Zaramoth.

After the protagonist earns freedom, they discover that they are infected with the Plague, a mysterious disease created by the Dark Wizards that drives its victims to insanity.

The old man explains the Plague, saying that it is caused by crystals created during the Great Cataclysm that give license to the souls of Zaramoth's army to possess the living.

[5] The expansion pack introduces several features, including an additional act (campaign), two hybrid classes based on existing classes, Dwarves as a playable race, enchantment-based "recipes", two pets purchasable at the act's main town, including the Pack Ram and Kohl Beast, and the PlayStation Portable crossover items to promote and to be used in conjunction with Dungeon Siege: Throne of Agony.

"[4] Detroit Free Press gave the game all four stars, saying, "It's a winning combination: the same great concept that made Dungeon Siege a hit now with new story lines, new features and improved graphics.

"[20] The Times gave it four stars out of five, calling it "a handsome game with a stirring soundtrack, with the potential to deliver weeks of very involving gameplay for hardcore followers.

"[21] However, The Sydney Morning Herald gave it three-and-a-half stars out of five, saying, "Fast-paced, epic and accessible, Microsoft's hack'n'slash sequel will entertain role-playing novices but disappoint veterans looking for more depth and innovation.