According to ESRB, this game contains: Animated Blood & Gore, Animated Violence
Parents should be aware that the game is rating 'M' for mature audiences. Diablo II isn't morally reprehensible compared to some of today's more violent games (profanity and sex aren't present in the game), but the bloodletting and carnage that ensues during massive battles will probably raise a few eyebrows. Many of the often mutilated dead corpses that often decorate the landscapes will probably irk as few parents as well.
Owners of lower-end systems and 56k connections will be happy to know that Diablo II—which utilizes sprite-based graphics—isn't very hardware intensive and should probably run smoothly on most setups.
Conversely, owners of high-end rigs will probably be upset that Diablo II isn't any kind of a technical benchmark for their hot new 3-D videocards.
Fans of the original Diablo should not be disappointed. Blizzard took time developing the sequel and it shows in the final results which is well designed and produced properly.
Fans of RPGs expecting elaborate and complex system or some sort of a sweeping storyline will be probably be disappointed with the action heavy and streamlined interface of Diablo II.
Fans of massive multiplayer RPGs like Everquest and Ultima Online won't find a similarly complex social system in place, but there is a large community of players present, and the trading element to the game keeps interactions constant and appealing.
I also have some advice for all gamers. Be prepared to lose a couple of nights of sleep, and if you want to save time, forget about the single player mode and jump right into online Battle.net game since that's where the Diablo II shines its brightest.