Hearthpwn

It's powerful, but I don't know if it's good enough yet. It just takes so long to come out, and most cards that summon or interact with treants are on the slow side as well. And the decks that give you that much time usually won't care if they are 2/2s or 3/3s.

It buffs many other cards indirectly, like The Forest's Aid, Cenarius, Tending Tauren or Garden Gnome, which should not be underestimated. Even Witchwood Apple is significantly better when you get 3 2 mana 3/3s. However, summoning Treants is still a bit too clunky and not quite strong enough. It usually takes too long/too much mana to get the synergies going, making it too slow to stand up against aggressive decks and too weak to grind out control decks. 

Still, I think this card has some good potential. Maybe not this expansion yet, but if summoning Treants should get easier some day, or gets easier to include in other deck types, it's quite threatening to have 3/3 tokens for the rest of the game.