lampwithoutlight:

Well, I tried to picture his emotions through the movies and I came to think that I really don’t like his prince appearance at all because he lacked of character in that time. (Or maybe I just drew him bad)

I think Prince!Loki was very good at keeping his emotions under wraps, which is why his face appears so neutral, even bland. Then after what happened in Jotunheim, his facade pretty decisively cracked (along with some other things).