I dont have the math behind the new set-bonus
Item - Death Knight T20 Frost 2P Bonus E Obliterate has a 10% chance to deal damage a second time.
Item - Death Knight T20 Frost 4P Bonus When Obliterate deals damage, you have a 10% chance for your next Frost Strike to consume no Runic Power.
but the bonuses feels really booring.
This doesnt do anything, does not change any rotations or help out the rotation. Rather it screws up rotations from time to time. I would say its a booring change.
I guess its time for Unholy to shine soon again :P