I'll happily admit that of all of Blizzard's current projects, "Diablo 3" is my most anticipated so far. Having played "WoW" for a year and quit with a fair amount of withdrawl, I have no interest in returning to Azeroth. And, well, I'm too slow (both in the mind and body) for "StarCraft 2." So that just leaves "Diablo 3." Unfortunately for me, and many others, it's "Diablo 3" which will probably see the longest wait.
At BlizzCon 2009 it was revealed that Blizzard's two releases next year will be "World of WarCraft: Cataclysm" and "StarCraft 2." "Diablo 3" will likely see a 2011 release, which basically takes it out of the running for games I can genuinely be excited about.
Also unfortunate is how Blizzard seems to release awesome-looking gameplay footage of their games several years before they actually come out. Here's the latest example: 10 minutes of the newest "Diablo 3" class, the Monk, kicking ass.