Keep in mind that I’m only at the beginning of the game, but with that said:
The story is so much better. In Skyrim, as in all TES games, you either follow the mediocre main quest, or settle for a bunch of other side quests, some of which may turn out to be interesting (see Dark Brotherhood in Oblivion, for example), while most will be just as mediocre. At the moment I want an interesting and focused story, rather than a collection of little quests that frankly bore me to tears.
In The Witcher 2, the characters you encounter, allies, enemies and neutrals, are so much better realized, infinitely better voice acted, and far more appealing to the eye (they are not fugly like people in TES games are, even after mods to improve that). They also move around and act like actual people. All through the conversations with a certain Jarl in Skyrim I kept thinking, when will this guy change pose from “I’m relaxing on a couch, stoned” all the while discussing extremely urgent, unprecedented events. He never did. The characters in The Witcher 2 are emotive, expressive, the conversations almost feel like little plays you participate in.
The combat in Witcher 2 I tolerate at best, just as in the first one. Even so it’s more fluid and less awkward than Skyrim’s (and really, Oblivion’s too). Although if this were my first Bethesda Combat game (Fallout 3/New Vegas melee combat counts here too) I probably would have preferred it to The Witcher’s.
The game is beautiful. I don’t mean just in the graphics department, Skyrim has that too and it’s not enough. I mean the art, the locations, the environments are very pleasing to the eye, while in Skyrim I constantly found myself thinking how dreary this place is. It largely has to do with the color palette, which in Skyrim is brown and gray in much of the places, and that has to do with this essentially being Scandinavia, but I can’t help the effect this has on me compared to the bright beauty of the Witcher 2.
The setting in Skyrim is basically Renfaire Viking Land, which rubs me the wrong way. The setting in Witcher 2 is so much more interesting: the world is more brutal, the people are all realpolitik all the time (aside from your very few friends). I have a hard time expressing this difference, but let me put it this way: Skyrim is Xena the Warrior Princess, while the Witcher 2 is Game of Thrones.