A new Arena balance update was just issued. The idea is to lower the appearance of good cards in nerfed classes and higher them in buffed classes, so the winrate of every class gets close to 50%.
- Nerfed: Hunter, Rogue
- Untouched: Mage, Warlock
- Buffed: Druid, Paladin, Priest, Shaman, Warrior
Read more… (official Hearthstone forum)