Hearthpwn

It will be good in midrange decks like midrange shaman with, as someone already pointed out, Al'Akir the Windlord. Al'akir alone provides taunt, windfury and divine shield. Aggro and Midrange paladin also play divine shield and taunt with a card like Tirion Fordring and, if this card would be more interesting to try out, Bolvar, Fireblood with just divine shield.

The better part is that it's an absolute amazing card for midrange orientated decks. Aggro can see some use of it, but I wouldn't be 100% sure of it. That would require some testing.

This card, however, is simply worse for control, combo and tempo decks. Control simply cries, it doesn't do that much. Combo doesn't care and doesn't play windfury, taunt and divine shield. It may use Lifesteal, but that will be marginal or with spells. Mind you that this card only checks minions, not spells, so spells like Spirit Lash won't work. Another thing is that such a minion has to be in your deck. Aggro and Midrange running out of cards is very rare, but it happens much more with Control and Combo decks. Then it would indeed be a dead card if it's at the bottom of your deck.

Tempo doesn't have any of those minions and it doesn't give a tempo advantage. They are also more spell orientated than minions, so the value of minions played have to be high.