I disagree. The slider makes me jump between sliding and reading the value below. Since it's purely qualitative - I don't see anything wrong with discrete values.
There's also the opposite route; where you manipulate the face and not the slider.
I remember reading some article about it where I think there were two axis; love vs hate and weak vs strong emotions I believe and by moving over the face you would see the facial expression change and select it by clicking.
That could also be an interesting approach for this...
