My thoughts on Mordekaiser after playing him more, lengthy read I'm sorry:
tl;dr my suggestions, revert W, revert the base MS, put some power from his Q back into his E and work on his ult a little more
Q is better, but it's a lot less interesting. Damage is WAY too front-loaded onto it which makes me think it's the only way they could make it feel powerful. I feel like I could be playing Olaf or Shyvana when I'm doing it, except I'm giving up more spread-out damage for up-front burst. I always thought it was much cooler being described as him slapping you so hard that everyone near you will feel the pain. I wouldn't mind some of the damage being slightly traded off for this capability on the second and third hits, which would also improve his massively reduced waveclearing potential. Additionally, it needs to be bugfixed so that it applies on-hits properly on the second and third hits.
His 325 base movement speed is just stupid. You can't punish a melee champion for building movespeed items so he can get into melee range easier. Can you imagine if Udyr or Singed or Volibear or Olaf or literally any melee champion with no means of immediately closing the gap besides running at you were given this change?
W just flat-out sucks. I hate this ability now. The passive is invisible power, it's ally-cast only (which breaks the immersion of game feel, as it has no business or reason to be such), the damage is down, you don't get resists, and you traded ALL of this for a measly heal and the XP passive. This just needs a total revert with exception to the heal, though I can definitely live without it.
E suffers because of Q's raised DPS. Its lowered damage makes it much less satisfying to use, especially on his AD builds that Riot seems to want to be pushing. While it still hurts hard on his AP build, it could use a little damage tweaking. I think slightly upping E's AP ratio would keep his AP build a strong alternative.
R is moving in a good direction. More power in the ghost, less power in the stats, and dispensing that power to the rest of his kit. While I feel the dragon is FAR too powerful to be healthy, it's vaguely countered by his inability to ult anyone until it dies. Perhaps a cooldown or grace period between dragon's death and his ability to ult if it isn't already on CD is necessary. I think the range nerf was too harsh, though.
Passive shield is much better for all builds except raw glass cannon ones, but really he should always have at least one HP item and a few that grant him resists -- he can grab a good chunk of all of these stats without losing his offensive power.
I think that unless W gets reverted, this rework will be a flop. With the rest of his new kit, Mordekaiser is actually much more than a "cool whacky new idea" for a bruiser bot lane -- he can go anywhere and work. His jungling power is actually very potent now, he can go mid lane, he can go top lane, and he can even go bottom lane. And on top of that, he can build anything and he'll still be able to work. I know Riot, for some arbitrary reason, decides to hate AP Mordekaiser (despite it being the obviously superior choice for gameplay and lore) but right now, he can still work pretty damn well. If tweaks are made, I think a lot of opinions could be swayed from this being a terrible rework to one of the best.