>Kings rock, quick claw, bright powder, scope lens, other hax based items
Pretty self explanatory. They can be fun to use as a novelty, but not in the long term. When fighting against them it turns the game into a joke, regardless of who wins.
>Eviolite
The fact that it's based off a hard percentage and doesn't work on a principle of diminishing returns means that the amount of pokemon it enables is very limited. Pretty much all you get is high defensive statted walls/utility stuff like Chansey/Dusclops/Porygon. Also makes knock off way too important a utility to have on your team. I like the idea of a powerful item that helps make NFEs viable, but I think they could have done a better job than eviolite.
>Leftovers
I'm not nearly so sure about this one compared to the other two, but the item is very splashable on many types of pokemon and it kind of hurts item diversity (especially with regards to utility items). Lefties is the only item I can think of off the top of my head that you can have 4+ on your team and have it make 100% sense. Health regeneration is a good mechanic, but I feel the item is just so boring. I think black sludge is lefties done right- it has some interesting applications and restrictions. If lefties were to be removed and be replaced by more nuanced versions of health regen per turn, I can't say it would be better, but I'm open minded to it.