Is William Dafoo a good actor?

I don't think so.
Very un-natural.
I can always tell he's acting, and he takes me out of the movie.

Given that he's largely a character actor (as opposed to the 'lead') he's utilized pretty well in movies.

His gamut is either procedural or psycho?

Yes, generally he’s pretty great.

He was amazing as Sgt. Elias in Platoon, I think that might be his greatest performance but Platoon was a great script.

In Boondock Saints he was a bit off, a bad performance in a so-so movie.

The guy has around 150 projects under his belt and is a dependable character actor type, he oozes intelligence and toughness. I like Dafoe a great deal, he’s a Golden Boy👍

Very good actor!

Yes he is. There's a reason he keeps getting work in Hollywood. He's good at his job and he's very likeable and easy to work with behind the scenes. He may not be handsome, but he makes up for it with talent and being nice. He's played a variety of characters too. It's not everyday you meet a guy who's played both heroes and villains in his career, and did both very well. He's even done voice work! Just ask Pixar.

He's a superb actor. His performance in The Lighthouse is widely hailed as a career best. I find it hard to believe that despite being nominated several times he's never won an Oscar (incredible that he wasn't even nominated for The Lighthouse).

yeah he is badass

Very good actor.