No More Heroes's gameplay was fun mostly because of the motion controls and inventive level design gimmicks. If you played on a regular PS3 controller, it's kinda monotonous.
The bossfights were great, the story was creative and fun and well, it had it's owl deal of metalinguistic criticisms. It has substance, even though it sure isn't a DMC in mechanical depth or a Killer7 terms of narrative. It's indeed a simple, but great game.
Meanwhile Killer is Dead is… Ok.
The mechanics are deeper and the combat is satisfying. This, until you get the timing and start dodging everything, abusing the slowmo system. The game is really forgiving with the timing and it's really gamebreaking. You have tons of combat options, like shooting, but i felt like foi only use them when it's mandatory. While the mechanics have more depth, the gameplay design seems less coherent than NMH.
And then… We have the story. Killer7 had a confusing story? For sure, but this was really something that helped to build the atmosphere, and it wasn't meaningless: we had this slow but tense gameplay in a surreal plot context. And when you look at it: everything in Killer7 had a symbolic reason to be in there. Mostly for it's themes, worldbulding or character developing.
Killer is Dead looks more like a failed homage. The weird stuff is mostly bonkers and meaningless, gameplay is fast and this makes the entire dreamlike stuff less of a focus. The story is convoluted for no reason at all.
Suda51 didn't even write most of the game. He didn't even direct it. But, like any Grasshopper game post NMH:Suda slapped his name on it and hoped for his fans to buy it.
It is by no means a bad game, but sure isn't comparable to The Silver Case, Flower Sun and Rain Killer7 or any other earlier Suda51 game.