Hmm, well, "most" promising is a strange concept as it seems to carry some implicit knowledge or at least sense of what the games will be like. None of the games mentioned stand out as obviously more promising - so I'm thinking they could all be great games.
If we're talking potential, then I think the one that COULD turn out to be the best of the bunch is the Alien CRPG from Obsidian. I've been dying for a decent game set in that world for a LONG time, and a CRPG is just icing on the cake.
Dragon Age died to me when it was announced as singleplayer only, as I'm not really too excited about yet another fantasy solo game. I don't expect much from Bioware these days, especially not after playing Jade Empire and Mass Effect.
Diablo 3 will most likely be a very good hack and slash game, but after the core of Blizzard North left - I'm not convinced it will be a true Diablo game.
Risen is probably my second on the list.
Beyond that, I don't immediate recall anything too exciting coming up. Darkfall, perhaps, but that's an MMO.