@Mason Mouse  

 
huh, that explains so much on why i have trouble reading human expressions and recognizing faces… i should go out more

Animation often relies on exaggeration to get the point across. We’re used to the subtleties of human faces, not ponies. Or dragons. Exaggeration assists us in understanding.
 
And it’s funny.

You are not the only one. 4chan tends to hate it to.
 
As for myself, I think you’re just looking for a reason to be mad. What do they add to the show, you ask? They’re silly as hell. That’s what they add. Furthermore, they’ve been making silly faces since Episode 1.

they’re hilarious  
i love the rarity one down the bottom

A lot of them remind me of Momo.

Pinkie’s one on top is just plain creepy.

That will always be my favorite Applejack face