Their hero ability damages the face. This prioritizes aggressive decks, although Midrange decks are also very popular. They have Beast synergies so removing Beasts should be a priority. Their ability to wear you down with hero power means every single point of face damage you can prevent counts.
The class's current play style typically suffers in the long game. Its hero power does nothing to affect the board. If you can bait out its burst potential and Silences on low priority targets, then it will have trouble finishing you.