The thing I've noticed, besides the drastic change in shape of the lips themselves, is that there's a lot less "meat" happening around the mouth area as well. Like the face has been smoothed down a lot with lips plastered on top, whereas before there were defined fat pads around the mouth that would plump up that area and/or cause dimples.
It was the first thing I noticed missing (besides the reduced nose smudge) on my fem miqote face 4, she used to have a kind of beak-like quality to her nose to top lip area that gave it this plush look that's just gone now