Excellent in my opinion.
He strikes me as someone who very much has his own vision and adheres to it. From writing his work to being at the helm as director, he's one of those guys who pretty clearly leaves his own stamp that distinguishes his filmography.
It helps that I thoroughly enjoy quite a few of his films. I think that Boogie Nights will always be my favorite of his. But even the stuff that I don't particularly like, such as The Master, I would still deem as really well done from a technical and acting standpoint.
He's one of those filmmakers that seems impressively adept at both securing terrific performances (it helps that he works with a stable of great actors) while also being very technically and stylistically skilled.