I raided Meta/ruin when Wrath first appeared.
Immo aura is a huge boost to DPS. ticking for over 800 per second to all mobs in range if I remember correctly.
This may have changed.. my gear certainly has since then.
Whatever its damage is it certainly is a brutal ability and is one of the defining points of Meta.
Its also hilarious in PvP when DK's pulls a seemingly helpless lock to them and ends up with 800lbs of burning purple demon land on them. that or rogues throwing themselves into an oven
Shadowcleave.. To be honest i did not find very useful at all.
The charge primarily closes distance niec and fast for the immo aura.