Unless you're drawing explicit realism, in my opinion, expressions should be exaggerated to some degree. If you aren't doing a 1:1 recreation, the point is to get the FEELING across. Try making the expression you want to draw and feeling how your face pinches and stretches.

Skin doesn't just "disappear" when your face moves it around --- that's where wrinkles come from! Pay attention to where your skin creases when you emote, and use it to your benefit. It's a fine line between overdoing it and underdoing it -- find your own balance.

Ultimately, every expression has a little bit of push and pull, unless your face is completely neutral (and even then, there are still some wrinkles...). Learning to think of expressions as actions and reactions is VERY helpful in learning to draw them without needing a reference, and in learning how to stylize and push expressions based on references as well!

I think a lot of people end up with stiff or unexpressive emotions in their art because they're just trying to recreate a picture instead of understanding WHY and HOW the face is moving --- and it's a tough thing that takes a while to really pick up and learn. Hopefully is helpful in showing a way of thinking about it that can influence your process and approach to emotions!!!

Also, bonus: even without the lines, the planes alone still show a LOT of emotion.