I like him, but his movies aren't perfect. Requiem for a Dream ultimately failed to realistically portray his goal of showing addiction as something that anybody could do, considering the unrealistic direction. Pi suffered from that same bout of unrealism. The Fountain also didn't fair too well, among critics or the box office.
Overall, I think I like Christopher Nolan or Terry Gilliam better. But, really, it's better to pick out excellent movies than excellent directors. Directors will not always be consistent with greatness.
Rosalina: But you didn't.
Robert: But I DON'T.
Rosalina: You sure that's right?
Robert: I was going to HAVE told you they'd come?
Rosalina: No.
Robert: The subjunctive?
Rosalina: That's not the subjunctive.
Robert: I don't think the syntax has been invented yet.
Rosalina: It would have had to have had been.
Robert: Had to have...had...been? That can't be right.