A much-improved version of the hack n' slash classic that was Diablo.
Although the graphics are somewhat dated, you quickly forget the slight blockiness of your Barbarian when you dive into a horde of monsters. Diablo 2 is at its heart a character building game, and the skill system allows you to really experiment with different playing styles, even when only playing one class. For example, the Amazon can be played as a jabbing melee goddess or a mistress of missile weapon mayhem. The classes are well balanced, especially after you patch the game up to v1.06.
Although the graphics aren't the best, the cinematics, voice acting, and sound effect are awesome, especially in several sections of Act 2.
This is one of the few games that I have that I can come back to in six months and still enjoy, whether playing single or multiplayer.
The one problem with the skill system is that it rewards you for specializing in high level skills at the expense of developing low level skills. Some classes even have a few throw away skills that are only useful as a means to get to the better skills. For example, the Necromancer's Skeleton Warriors never get very powerful, and so it is useless to build this skill up at all since the golems, revived creatures, and skeleton mages are so much better. If I really wanted to be a master of a skeleton warrior army, I should be able to do it and survive at high levels.
Another thing I don't like is that you are penalized too much when you fight monsters that are 10-20 levels higher than you are. In an attempt to balance the multiplayer game so that a high level character couldn't join a party of low level characters, kill everything for them, and have them advance quickly, you are penalized in xp per kill if you are way above OR BELOW the level of the monster. So if you manage, like I did, to finish the game at Nightmare difficulty when you are level 38 or so, there is no way you can survive or even gain any xp in Hell difficulty until you gain 15-20 levels! The game just slows down too much after level 30 or so.
The Bottom Line
A great hack and slash game no matter how you play it. Despite what Nethack fans may tell you, this is not just "Rogue with nice graphics and sound". It is a different, more entertaining, and much less frustrating and obtuse gaming experience than its text-based predecessors.