Their clean parts are almost spoken word, but yes there are a few exceptions.

I remember when I listened to a Katatonia album, found it incredibly boring.

I don't think there's any extreme metal that utilizes even mostly clean vocals

IT'S A COAT HANGER!!! regardless of what he tries to tell ya. (knitting needle)

I love screaming vocals, yelling vocals, even some growling vocals. Just can't get into bands that feel they need to make cookie monster **** 100% of their vocal style.

It's kinda like when Kirk Hammett decided he needed to use whiny wah wah **** on every single one of his solos.

^what artist that you're into would you say has the "harshest" vocals

Devin Townsend and Pain of Salvation. But neither do it all the time. Which is why I like them.

I was just curious.

Do you like Strapping Young Lad

Yes! Have loved Townsend since he did that album with Steve Vai in the early 90s.

SYL have some seriously destructive stuff that I love

That is just ... silly.