I've still got mixed feelings about this discussion.
While I think Nolan's films are, in general, intelligent and well-made and engaging, he doesn't come close to some of the filmmakers of the past 20 years. Coen Brothers, Richard Linklater, Paul Thomas Anderson, David Fincher, Wes Anderson, Ang Lee, Guillermo del Toro, Alfonso Cuaron, Sam Mendes, Darren Aronofsky and many others are all leagues ahead of Nolan in terms of their films. The difference is that, for the most part, they have not connected those intelligent films with the audience on quite the same level as Nolan.
And if I'm gonna say that Nolan is a true great for managing to do that, then I'd also be putting Peter Jackson ahead of him.
I suppose the truth is, it's hard to say who is an all time great when they are in the middle of their career. Give it 20, 30 years and we'll have a better picture. For now, I don't think there has been another Kubrick since Kubrick.