I wanted to put this under the New player experience post at first but on second thought better put it here.

So basically the idea is to give players the opportunity to rate all the cards they have and display the average rating in the merchant screen.
In addition to that, it would be good to put a list of synergic cards as well as counterplay cards (also rated by players). This can be a good way to help new players build decent decks right from the beginning.