I have played new Mordekaiser, and he feels too simple
He is heavily lacking in an appealing nuance that helps lessen that "unga me club you" thing that juggernauts oft get stigmatized for. He is very, very reliable and its almost stifling in how guaranteed he starts feeling after you get used to his E.
What I mean by nuance is that most other juggernauts have some kind of depth to their playstyle that at least makes it fun to get up on somebody and bash them like a cave man. Darius plays around 5 stacks before he has his steroid and his Q outer range and R resets. Illaoi fights around her tentacles. Aatrox fights around his sweet spots. Yorick is pretty mindless bashing but he has to PvE for half a minute before he can throw E at you and go full chimp on your head.
Mordekaiser gets his passive up with any 3 instances of damage from his kit, and then his passive aura is up for as long as he's fighting. In addition to that his primary steroid is completely passive and permanent, and only requires gold to scale it further.
Its not that he's almost Garen levels of simple, but I just don't really feel satisfied by the gameplay pattern I'm given; he doesn't have enough visceral satisfaction through stimulating visuals to make this simplicity work the way Garen does. And I asked my friends who also have PBE and they agreed that he feels very simple and statchecky.
I like a lot more about Mordekaiser than I thought I would -- him having a pure defensive tool and good utility is fantastic change of pace and a direction I hope continues -- but currently the sum of the kit is offputting to me.