I'm still in chapter 1, as I didn't play much.
Certainly it looks way way better than Witcher 1. Most noticeable change is the combat. No more click and watch combos, you do combos yourself with left click being quick attack and right click heavy attack.
Other major improvement is that opponents now hit you during you're fighting another, not like the previous game that they used to watch you slash their friends then attack you. That made the combat more fun, as you have to dodge to live a simple bandit fight
Not to mention graphics improvement. I play using high settings and it's really impressive. Ah almost forgot. Now every single word you say influence the flow of the game. Your decisions matter.
Till now I'm thrilled having this game at home, shame I will not be home in the next 3 days. I will say more when I go deeper.