Personally I think that the artstyle of the flashbacks in The Witcher 2 was much more characteristic, sharp and reflective of all the madness around. It was also a fun nod toward the unfinished comic book that Geralt's original designer wanted to make, where the artstyle looked pretty similar (you can see a heavy inspiration with Simon Bisley work). This one looks good, but overall it's seems to be pretty standard. When I watched it I was mostly thinking "well, that should satisfy people complaining about The Witcher 2 flashbacks", instead of "wow, that's really something". While the artstyle looks a little too "safe" for my taste, I will however praise the animation style. In the previous game it seemed kinda weird at times (Geralt vs. Aryan for example), but here it looks much nicer and more fluid.
I don't miss oil paintings from the first game (as some of them looked really ugly and not in a good way, like in The Witcher 2), so I still gladly take this comic books style over it. Overall, it's good enough for me and I will have no problem if this is the kind of flashbacks we can expect in The Witcher 3.