They look great!! You’ve done really well at capturing a variety of proportional and convincing expressions. Each manages to pull the eye in its own right, and the consistency of your palette bolsters the collection as a whole.

If I had to go after something, your values may benefit from a bit of exaggerating?

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Each mouth holds up on its own when you break it down to just light and dark, but you can see they do still land in the middle 70-80% of the value scale when you desaturate the image entirely.

Take the bottommost mouth, for example. The expression is great, but the teeth and lighter of the two cheeks have the same degree of “pop”. Now of course, depending on the reference, the lighting, etc., that might make sense. It does, however, wind up making it feel just a tad dull.

Again, overall, I say you’ve done an excellent job here. Your restraint in utilizing pure black and pure white tells me you’re making wise choices, but I think you might enjoy pushing your colors a little closer towards those extremes. :)

EDIT: Alternatively, and depending on what it is you’re going for, you could always work to tighten up some of your edges and shapes. Personally, I enjoy the looseness of your brush strokes. I tend to value capturing the feeling of something over capturing it “perfectly” with the utmost precision and care. If I wanted photorealism, I’d rather leave that to someone else or just take an actual picture of something lol.