The plot and setting: In a gothic fantasy world, hell-spawned demons led by Diablo, the Lord of Terror, have started their second attempt at conquest of the mortal plane. You play as either a Paladin, Barbarian, Sorceress, Necromancer, or Amazon as you chase after Diablo, leaving a trail of dead demons behind you. The game is divided into four Acts, and there are incredible cinematics in between each act depicting Diablo's evil scheme.
Comabt: Unlike in the original Diablo, each character class in Diablo II is 100% unique, each with a great tech tree of skills, providing excellent replayabiltiy. The comabt is the most addictive thing on the planet, and you run through the dungeons clicking on anything you see. Whenever you die, you pay a gold penalty, and respawn at your base, albeit without your gear, which still lies on your corpse. SInce death isn't really a big issue, you can through tactics out the window and just have a good time whacking creatures with your sword, throwing spells at them, and chugging health potions.
Graphics: The graphics ain't that great, but who cares?
Cons: The game can occasionally get monotonous during long stretches of monsters with nothing in between (Act III).
Overall: An amazing game with addictive combat, a wonderful apocalyptic story told through fantastic cut scenes, and tremendous replayabilty.