Sequiro: It added the Monk class to the game, added some items (including new potions) a new quest chain.
And no ones mentioned it OH SO THANKFULLY speeds your character up in town. Between loading and the fact your character only walks at a snails pace in Diablo, bad enough in dungeon but at least the combat there can distract you. But even worse in town. Hellfire makes your character practically sprint around in town.
That being said, it did have a sort of generic feel to it. I was so pissed a few months ago I saw it in a used media store for 10 bucks didn't have the extra cash at the time for it. (I was there selling some books for gas money lol) went back a few weeks later and it was gone.
That said I have problems getting Diablo 1 to run right on Windows 7 anyways. I still in some ways feel Diablo 1 was more memorable than Diablo 2. I enjoy the music a bit more, that damn town theme will forever be etched in my brain. I enjoyed the conversations.. and Wirt, classic quest lines like The Butcher. Ah great game.
I unlike others though played it back in the day not on PC. But on Playstation
Create a Diablo.bat file with the following contents in the game folder and run the game from this file instead the exe..
It force closes Windows 7 Explorer which causes the issues because of incompatibility with the palette swaps the game uses.
This also works for any old game that has color issues.