Old W was awesome.
Throw it on Minions if you are too low to get in the fight itself. Decent amount of resists. It was a very good ability that allowed Mord to duel extremely well and improved his team fighting since he could make his Tank even harder to kill.
It was simple and hard to notice, but it was very reliable, unlike the new one.
Not to mention, more pushing power! You can never have enough pushing power when you are Mordekaiser. New one cant push for shit without an ally since his attack speed got gutted and he has a grand-total of ONE AoE skill.
Also, Creeping Death had a lot of metal particles that made you feel extremely badass. The new one doesnt have anything since CertainlyT removed Mord's metal from everything other than his model.