Not a big fan of the black outlines + aliased lines + cell shading mix.
I think either normal line art should be introduced or he should add more values to the shading because this current mixture of methods makes everything look kind of flat, which is genuinely fine in most cases but if you're drawing inflation selling the size and shape should be your top priority behind making the subject attractive to look at.
It also looks like he draws the eyes first, then the head around the eyes, which is why a lot of the time the faces end up looking kind of offputting or a bit strange. Would highly recommend drawing the head shape before drawing the face or hair from here on out. (no I'm not saying big eyes = bad, stylization is great but not if you're skipping fundamentals)
You can handwave this is "style" if you want, but if he listens to me his art will look better so it's his call I guess lol.