I've been playing it for the past 3 days and I absolutely love it.
The graphics are phenomenal and the gameplay is typical Witcher gameplay if you've played the previous ones you'll go in expecting about the same. I'm not a fan of the keyboard layout so I'm playing with my Xbox One controller instead.
I can't speak on the performance for those without high end cards though provided you are playing it on PC. It runs great on my setup but I don't recommend using Nvidia's HairWorks. It likes to drain your FPS.
Anyway, it's a must buy for me. Even if you haven't played the previous Witcher games, you will still enjoy and understand this one. There is an option to 'simulate' a Witcher 2 save but I didn't go that route. You also have the option of importing your Witcher 2 save provided you are far enough into the story.