More of the same, and that can be both good or bad...
1.A lot of game content: huge areas chock-full with monsters and items;
2.Cool, imaginative, well created and animated monsters, with great sounds;
3. Incredible cinematics (the best in any game so far, and sure worthy of some kind of award...)
4.A whole lot of items, armors, weapons...
5.Skill system, which really adds a lot to character customization;
2.Gameplay that is, with the exception of the skill systems and the added classes, identical to that of Diablo 1; and this is a double-edged sword, meaning that if you liked D1, you will love D2, but if you hated D1, you'll feel the same way about D2.
The Bottom Line
An improved, polished, and simply better Diablo. If you loved the first, you will certainly love the second. If you hated the first, well, don't buy this game. Personally, though, I had a hell of a lot of fun with it...