What could Skyrim learn from The Witcher 2?
Well... it's difficulty for starters... TW2 has you using your full arsenal to be effective on the normal difficulty. Hard is even harder and insane is just that... insane. It doesn't hold your hand, it's up to you to learn the depth of it's combat, learn about your enemies etc (the first true boss you fight in the game can kill you in two blows on normal, in one on hard). I'm one of those people that likes it that you can't just drink potions in combat, you have to think ahead and prepare. Now I'm not saying Skyrim should do the same things (like not being able to drink potions mid combat since I'm sure a LOT of people will dislike that), but make combat more difficult, challenging and rewarding.
I like the way the characters feel, they feel authentic, they don't feel like stereotypes (*cough* DA2 *cough*), they feel normal yet exceptional and interesting at he same time (by comparison OB's characers are uninteresting and bland apart from a few of them like good'ol Sheo). I'm constantly questioning their motives and only trust one person in the game so far (Triss). Apart from Geralt's wish to catch the king slayer there's a web of political and racial conflicts surrounding that plot.
Quests are very interesting. Hangover is the best quest ever
Choices do make a huge difference as to how the game plays out. And it's not all black and white, you have to think about the consequences, maybe that person you saved will betray you later on or maybe you'll get a pretty awesome magical item from them (TW2 players know the events I'm referring to), maybe you choose to turn your back on things and it will come back later on and bite you in the ass, maybe you'll be able to avoid a bad sitiations by doing so etc.
Graphically it looks great. Best looking RPG I have ever played. Aesthetically, the attention to detail is amazing.
Unlike The Witcher 1 it actually feels mature without failing by trying to hard, the six scenes are erotic but feel natural, you don't stumble across them every 5 minutes. I'm not saying that Skyrim should have six scenes (blacked out or not), no. What I'm saying is that if it's an M game make it feel like an M game.
The hunt for rare crafting materials is awesome. You can craft a LOT of things, I hope Skyrim features such depth in the crafting aspect.
Now, what should Skyrim not do?
Enemy combat AI (not just the monsters, even the humans) isn't very good in TW2. But the again Beth can't really claim they did a great job with combat AI either.
It should stay faithful to it's sandbox approach of go where you want and do what you want.
Using inventory lists... it's annoying as hell. MW's grid system inventory was informative and easy to use.