I love the use of wrinkles! My favourites are the third and fifth guys. They could be the same age, but one is obviously a much more jubilant fellow, with his crow's feet. The other has those frown lines that tell you he's a bit of a pessimist. I also like the way that your characters have small eyes.
Usually I don't like small eyes, but you make them small and yet make sure they have colour. I think that's what bothers me about eyes, is when the artist doesn't give them colour. You also do a lot with nose shape and mouths, as well as brows. It's obvious you pay attention to all the differences in how people look, the little details that normally get overlooked, such as people smiling differently or brows being arched differently.