Arno’s alien has a unique design and he has put quite a lot of work into the detail [especially the eye] and the smooth shading.
One problem with the shading is the lack of contrast. It’s very soft and timid and therefore not helping define the volume of the green body shade. It still looks rather flat and two-dimensional. Stronger shadows and brighter highlights could bring out volume and texture.
The nose and lips [being the same colour and shading] are not that distinguishable. Their connection to the body feels odd due to the ‘outline’ shading.