SammjuBognir: I noticed that when starting both games you start at the same town. My question is this, is playing Hellfire playing the same game as Diablo except with added material? If I choose to play Hellfire first can I play all the material in Diablo or do I need to play both games separate? I'd like to do a play through of the first Diablo but don't want to play through it twice just to play added material from Hellfire if I can just play Hellfire and play the Diablo storyline as well.
Diablo on its own is the quintessential ARPG that started it all. It is worth playing before giving Hellfire a go. I personally prefer Hellfire at this point in time because I have already had my fun with the original game. If you are jumping into single player do the original game first, and if you like it take Hellfire for a spin. There's a pinned post in this forum for Jarulf's Guide which goes into extreme detail for both games.
With all of that said... yes, in the end they are pretty much the same thing with Hellfire just adding a bunch of stuff on top of the base game. And there is a lot of people around that will tell you more doesn't equal better and Diablo is better than Hellfire, but also Blizzard officially patched Diablo for a lot longer after Hellfire was released, and essentially ignored Hellfire and never recognized it as an official expansion. Which is why you can't officially play multiplayer with hellfire, however if you're playing Single Player I'm not sure how much that matters.
Anyway, I hope that helps you make a decision. Take care.