Witcher III has been announced. Planned to be released "sometime in 2014".
The biggest changes include: Open-world, bigger world (40x of W2), more in-line with the novels, greater focus on "Witcher work", new engine, next gen blah blah.
Slightly outdated full list of changes here. The change from the game being semi-open chapter based to full open-world is one that both excites me and worries me. It worries me because it's quite hard to craft a game which has an open-world that feels alive and responds to player interaction. An example of a game that completely balls'd this up this aspect is Skyrim (or any modern Bethesda game really), although it has decent exploration the world felt completely flat and lacking any player interaction on the world at a macro level.
The Witcher III seems aware of this and apart from the common stuff like weather/day-night cycles affecting monster spawns, plan to implement stuff like quests having deadlines/endings that can end with changes to the world such as bandits invading a village. There's also a storyline dedicated to playing imperial politics!
Combat seems to be getting an overhaul. The developers want to move away from roll spamming that was so common in W2 to a more finesse model focusing on parries and pivots.
There also seems to be a greater focus on "witcher work" which has me extremely excited. I like the idea of having the study the various monsters in the game to understand their weakness, behaviour and interaction with other creatures. This is much more like the novels which had had Geralt having to study the monsters ahead of time so he can use his knowledge to access the threat, it also makes that first play-through extra special.
I personally get a Monster Hunter/Dragon Dogma/Gothic/Skyrim vibe from the current planned features. Let me tell you it's quite an awesome vibe indeed.
The most important and best features by far are as followed:
No level scaling.
Geralt has a manly beard.