Hearthpwn

This is something I have been wondering about especially when new cards are first being revealed in upcoming expansions. I have noticed that whenever new cards are revealed in each new expansion, before the card has even been released a lot of people say that the card is garbage, it will never see play and that it will be the worst expansion ever. I remember when cards like Piloted shredder and Dr Boom were first revealed, people actually called those cards garbage. So my question is when a new card is revealed, what would convince you that it will be a good card on your first impression without having tested it?