TG: IMO opinion, the original Diablo was better than D2, but if you have already played D2, you might not enjoy Diablo as much. Diablo's a smaller game, more simplified, and the graphics are about the same. What I miss from the original Diablo are the pack of acid spitters that would be sitting around a corner. You never knew what hit you. I also liked the hiddens, which would materialize out from under the floor and suddenly surround you. Plus the ending is a lot more intense with the original. In D2, you go at it 1 on 1 with Diablo. In Diablo, there's Diablo and about a hundred mages all firing off fireballs at you, not to mention the death knights. Some of the uniques were cooler too, like the "Gotterdammitsdark" properly know as the Gotterdamerung helm. Very nice helm, but it did -2 to light radius. When voyaging through hell, it was really hard to see wearing that thing.
<Edit> if you do try the original Diablo, don't play it on bnet. Wayyyy too many hacks and pkers there. Not to mention autokill =(