The 4K is alright.

The colors are a touch muted and duller.

Looks better than the blu-ray I guess but not a superb 4K release. From the comparisons I've seen some of the previous blu-ray releases have better color correction. Though the HDR and superior detail help make this an improvement overall, probably.

Fulci's 4Ks have been middling thus far;
The New York Ripper was decent enough, though a bit teal.
The House by the Cemetery was pretty good.
Zombie was brilliant!
City of the Living Dead as mentioned is just alright.

Fingers crossed the upcoming The Beyond 4K is a great release!

Argento's 4Ks have been so much better;
Suspiria is sublime! One of the best 4K releases.
Tenebrae is brilliant!
Phenomena is gorgeous!
The Bird with the Crystal Plumage is superb!
Deep Red is fantastic!
The Cat o' Nine Tails is pretty good.
Four Flies on Grey Velvet is pretty good too.
I didn't get Two Evil Eyes so can't comment on that one.

Fingers crossed Inferno and Opera get 4K releases soon.