I really like the character designs. It is full of character and personality. The colors also really lends a lot to the expression.
My crit would be that the style doesn't feel unified, especially in the first two. For example the shadows is really sharp and well defined solid areas while the highlights are broken with soft graduations both of which are really neat compared to the very messy line art. I know that sometimes a deliberate juxtaposition is deliberate but I don't think it works well here.
The lighting is also inconsistent though this might be artistic choice. The shading of the face kinda indicates that the figures are lighted from the right side with the shadow shading the left side of all the figures. However we got a very large and strong highlight on their jaw with can only be achieved if the figure is lighted from bellow.
There are also some perspective issues. I know is a cartoon/anime but still. The first picture have features that seems to have mixed profiles (front or three quarters). The eyes and the position of the neck as well as the visible right ear indicates that this is a full frontal view, but the nose and the mouth (though in a cartoony fashion) are shaped and location associated with three-quarter views. It makes the figure looks a bit like a Picasso painting. The second portrait also have similar problems
Of the three, the last one is the best executed though it still have the perspective issue like with the right ear being visible in a complete three quarter view and the features that are too centered on the face.
Here is a photo of a head in front view and three-quarter view:
You can see what I mean when I said the perspectives are mixed. Only one ear is visible in three-quarter view for example.
Still, it is really well done with strong artistic sense.