The dwarfs power strike - oh yeah, is that a fun button! They've done well on that one - I think you are invulnerable during the wind up. Which is great when a zombie just decided to do it's grab rush in your direction and instead you see it slide around your charging up character, then get pounded by the hammer strike
I think I probably use it fairly inefficiently - you are probably supposed to beat 'em up (as if this game was some kinda beat 'em up!) a bit first, then drop the hammer. Since you will lose the weapon right after doing so. Though I improved unarmed attacks for precisely this reason. In fact I got unarmed attacks to 100% damage - really I should buy it up further. But again I'm still not sure what it does.
Anyway, love that one smashing button - and the way you watch a bosses health bar suffer during it!