About likes/favourites/thumbs etc, I agree with some that it is a great tool for bookmarking (that's mostly the way I've been using it on 8bc, for instance). However, I think it should be mandatory to add a comment in order to add a thumb/like/bookmark. It prevents laziness and encourages constructive criticism.
I like your idea of adding a comment to thumb, but there should be a word limit, so that people have to give you an actual comment, not just "good" "first" "sucks" "nice" I could see that becoming a problem if you made people comment before they could give it a thumb/like/arrow/opinion