hey man, all of these are looking really good, it's obvious you've put a lot of effort in!
but there are a couple of niggling things i've picked up on that seem like the root of a bad habit, and if we can get you out of them now... then great!
it mostly falls in the lips and the way you've textured them. almost everyone has this joker-like grimace going on. it's caused by two things.
1. dark outlines around the entire lip.
2. an upward curve and hyper extension of the corner of the lips.
i've done a small paintover to illustrate what i mean:
so a couple of things to bear in mind... the lower lip, unless there's lipstick involved, almost always blends into a natural skintone towards the corners, rather than having a harsh outline (note squall and zell vs rinoa).
for female characters particularly, but also heroic characters (in japanese illustration anyway) really push the filtrum shape to give the top lip that classical m shape. with lipstick, play around with colours a little more. using different shades of the same colour hue doesn't look quite right, so as an example i've used a brown shade, a red mid-tone, and a blue highlight in my example.
other than that it's all kickass man!