Skyrim is better in a few key elemnts:
1. The open world might be a lil bigger or smaller, but skyrim had around 150 indoor locations (dungeoen, keeps, forts, caves etc). Even if those were repetitve i didnt mind that much. Its jus ever step you take you find an interesting indoor location.
Tw3 has a huge open land but a fraction of the interesting indoors.
2. Freedom of choice on what an how to play. In skyrim you can be literally anything you want. Male, female, orc, elf, warrior, mage, a mix. Anything.
In tw3 you are very restricted to play like geralt, for obvious reasons. i dont mind being a specific character but you can use any other weapons (these hatches and clubs dont count. They use the same animations as the swords. There is just one weapon type in TW3), no shield or bows and what i really really miss fromt the witcher games is stealth. I really think stealth would have been perfectly right withe the character of geralt. A hunter should know how to stalk his pray or to overcome large groups of bandits be stralthly dispatching them one by one.
Skyrim had evrything. But mediocre quality.
3. Skyrim allowed you to do more. Sleeping in ins, talking to everyone, everyone can be questgivers, making food, etc etc. all these really contributed to the sense of immersion and place.
4. There are a lot of other things skyrim did and even well than tw3 doesnt but the main ones were stated above.
I played skyrim for about 3 years. I am LOVING the witcher 3 a lot but i doubt i will play it for even 6 months from now and THAT is the true test. Even though the witcher does things better, it does less and in the end it will hold me for less time and in the end it will have less of an effect on me.
My opinion about myself only