Diablo 1 you can just ignore. Diablo 2 is great. Expansion, battle.net, game guide comes with. Very cost-effective.
Gameplay: For Diablo 2 single player, it's a great rpg even now, 6 years after it's release. The quests are addictive. The enemies are challenging. It's awesome. For multiplayer, it's fun, but not as fun as single player for me. It gives me something to do with friends I don't see in person that much, and the gameplay is still good, but I don't feel like this is any objective or purpose to leveling up you character, especially with all the hacks available to anyone that wants a level 99 multiplayer character. But it's still fun.
Graphics: Obviously the graphics aren't the best due to 6 years of new graphic technology, but they were good for 2000.
Sound: Sound effects are good. Voiceovers are good. Wish there was rock in the background, but that's too hopeful.
Value: I recommend it, especially since it's cost-effective.