Officially announced by Square Enix. More info to come this E3.
It's said to be released on PC, but also on PS3 and 360 which is pretty awkward.
Obsidian are making this game (Alpha protocol, Fallout: New Vegas)
Dungeon Siege 1 was the first Hack'n Slash i've played. Even Diablo went after that. This game was really awesome and I spent hours playing it online. Never played its sequel since the disappointment could be seen on every player who tried it.
I don't know what to think about the 3rd one since it's also released on PS3/360. Well... It's not as if it was the first in its kind to be released on home consoles (see Champions of Norrath) but still... Wait and See.