Diablo II is the epitome of a hack-and-slash dungeon crawling game. After his previous defeat, Diablo now seeks to ally with Baal and Mephisto in order to enslave humanity once and for all.
Allowing you to choose one of five distinct character classes (seven with the expansion), and further customizing your character by choosing abilities and skills to specialize in, Diablo II really lets you create a fearsome creature of destruction any way you please. Many factors add to this game's appeal and addictiveness including tons of different loot (and even special sets of armor), free online play, and the aforementioned character customization. You'll want to get to "just one more level" or find "just one more weapon" before you realize that you're totally hooked into the game.
Diablo II was released for the PC in 2000 and is the sequel to the original Diablo which was released in 1996.