I really like the idea of this skill.. I gave it a shot and made it till about mid Terror before I gave up.
It seems completely non viable as a primary skill. The boss damage is alright assuming you can sustain spam casting it (mana cost is really high). Problem is, that damage doesn't scale at all into multi target. It's simply spread out and requires ramp up.
Is there a niche to make it viable? I imagine is scales well with crushing blow if you can stack a ton of it. It would work well with a slows target build?