With over 11m subscribers, World of Warcraft (WoW) is probably the only MMO that most people have heard of.
Set in a fantasy world where two sides, Horde and Alliance, battle for supremacy, WoW takes the standard fantasy genre and pumps it up to epic proportions.
Wrath of the Lich King (WotLK) is the second expansion, and increases the game's level cap from 70 to 80, as well as adding new areas and items. It also introduces a new 'hero' class, the Death Knight, although this is available only to people who already have a level 55 character. The Death Knight starts at level 55, but you must undertake a series of quests to learn your new character's abilities.
Blizzard seems to have been keeping an eye on the competition, because the expansion's player versus player (PvP) feature borrows heavily from Warhammer Online's realm versus realm idea. As well as adding a new area to the game world, WotLK introduces new PvP areas for the two sides to fight over.
The Player Achievements system is also familiar from Warhammer Online. You might gain a title or clothing item for killing a certain number of enemy players, for example. The rewards are purely cosmetic, but they offer a new way for players to gain bragging rights.
This expansion is a must-buy for existing players who want to keep up with their online friends, but serious long-term players may find the new content too easy. What's more, the rewards in WotLK render much of the previous high-level content redundant. Blizzard needs to tread a fine line between satisfying existing players and appealing to new ones, and WotLK shows they are starting to lose this balance.