I did another one for the skeptical expression, this time around you can see the character's entire body and it seems smaller than the face (Another form of perspective view).
One for a sad expression, the eyes look big and watery (glassy effect I would say like He is about to cry) or maybe like a puppy face.
Another version of a sad exaggerated expression, this time the character's mouth corners are pointing down on either side of his mouth. (This gives a stronger sense of sadness) when combined with the glassy look I Think)-This is more suitable for a sad expression than for a puppy face one.
I tried to draw a really exaggerated hppy face, as you can see th enoose is wider, the face is squashed rather than stretched and the character's has got a wider mouth.