The first Diablo game is still playable today even on the newest Windows 8 using different means. Either by using the ddraw.dll to window the game, virtual machine to emulate windows xp or by doing a registry fix to keep the colors in check.
COLOR FIX OPTIONS
You can play on line today, but good luck finding anyone to play with you. There was several mods and patches made to expand on the fun gameplay. I would recommend installing these mods instead of playing online unless you know someone who will play with you.
The Hell (unofficial)
This mod is one of the greatest mods available. Gives new NPCs, new quests, new spells, new classes, new items and cranks the difficulty way the hell up! Once you start getting the new items you will see why the game is more difficult. These newer items actually give you beast stats so you can survive on the later levels. I highly recommend giving this a try! WEBSITE
The only official Diablo expansion. If you install the unofficial hellfire patches you can make this mod multiplayer and unluck the bard player. But if you just use the 1.01 official patch it will unluck the barbarian class. Otherwise by default the new class is the Monk. There are just a few extra quests, items and a new main boss to go after. It also includes the Cow Level! This is still a fun expansion to try.
So that’s really about it. I recommend giving this game another look, and see where the Diablo III game started from.