I'm going to allow this random bump, just to add that WoW > D2.
If WoW and D2 were designed at the exact same time, with the exact same graphics, depth.. Etc, I believe D2 would be the more popular. I mean look, after nearly a decade it still is one of the most popular games on the internet. Sure, WoW launched in popularity crazily, but a lot of that credit comes from the reputation that diablo, warcrafts, and starcraft ( mostly the former ) had to offer.