Don't be going into it expecting a full on Skyrim style experience. They are like two opposite ends of the same spectrum. While TW3's world is gorgeous and brilliantly designed full of nice touches, it's not quite as alive as Skyrim's. For example most people are just called Peasant and they can have a monster 10 feet from them and not react at all. That's not to say it isn't a great open world, it's just not designed around it the way Skyrim is.
I love both games for different reason. TW3 could have been just as good a game without the open world, Skyrim couldn't. The story telling is where TW3 really pisses on Skyrim and most other games for that matter.
I'm not quite sure if this makes as much sense as I think it does.
I think TW3's world is far more alive than Skyrim'. Once I walked into Novigrad, it blew my mind how alive that city really is. It was truly breathtaking. Nowhere is Skyrim gave me that feeling that I'm actually in a living, breathing world. The NPC's are also just typical Bethesda, just walking, talking zombies.