Hmm, yeah, the changes to how the hair is handled are great. The original designs (at least, the ones shown on the front page of this post) have a very 'helmet' quality to them on account of being essentially one solid block. It's not so bad for Jazz and Paulina who have long hair, and Maddie whose bob haircut is sort of meant to look that way in the first place, but for Sam it looks absolutely atrocious.
Her eyes also seem to have been made quite a bit larger as well, which has worked well I think, it looks really good.
The slightly bigger noses are good.
One large and good improvement that I'm only noticing with a direct comparison is the new one has a much more proportionate face, maybe this is a large part of why I found the old Sam a bit offputting. Her face is all squashed up and her chin is ENORMOUS, she's got a major case of Key Face going on which the other characters don't really have to quite the same extent. It's not as bad when her mouth is open, but still.
Well, anyway, Paulina is also better, though not quite to the same massive improvement as Sam.
Looking back at Jazz, I think that's the closest, but the new one still has better clothing design and proportions so still a win. The flatter shading also kind of looks nicer. I'm really not that big of a fan of overly complicated shading on simple character designs, it looks a bit odd.
Also come to think of it, that Sam seems to now have purple leggings instead of fishnets may open up some sexy scene options if people want that.