It does seem strained, unfortunately... but it doesn't bother me as much as those occasions where he remains completely emotionless. You suddenly realise that this is not a movie.
Lol jk... but seriously don't you make your own face? Mine is fine... [well most of them, some are creepy as you say].. even Sheploo isn't bad. I like him smiling, makes me feel more paragon lmao.