The next Blizzard game is annouced on 19th of May, is it Diablo III or Starcraft 2?
Blizzard has started a countdown on their website.

Here's what I think of the games!

Diablo III:
Personally, I would like to have Diablo III very much! Diablo II was a great game, probably the best one I ever played.
Half the Diablo II-team quit working on Blizzard, and started their own companys, 
Flagship Studios and Hyboreal Games.

Flagship Studios has annouced their RPG this month (in alpha stage) , Mythos, it looks very similar to what Diablo III would look like. They could not use Diablo III because Blizzard own that trademark.
Mythos could be Diablo III, specially when I saw the well which worked exactly as Diablo II. When you click it one, you drink half, you click again, you drink the rest.
I don't like that Mythos looks unserious. The characters in the loading screens etc, has small bodys and huge heads, it looks like cartoon.

Starcraft 2:
The bets say Starcraft 2 though!

It would be a lot of fun to play the old Starcraft in 3D, with one new race (rumors!).
I really hope the map editor would be powerful, and you can create maps as those which were created for Warcraft 3.
On the Blizzard website, it looks like it's going to be Starcraft, it's dark and blue, on the other side, that could just be the colors of Blizzard.