Nolan's films are always complex and intelligent and thinking.
I do not think they are necessarily complex and intelligent, I think they rely on parlour tricks, similar to M. Nigh Shyamalan. He gives us the illusion of complexity through obfuscation, but make no mistake, because something appears
to be complex does not make it so. I have been able to figure out every single one of his films that I have seen in the first watch and often before they are finished. To me, that is not complex.
2001, as Panzer points out, on the other hand, still leaves plenty of room for interpretation of the ending sequence, even after many viewings. Stanley Kubrick was an accomplished genius in his own right, but when combined with the intellect of Arthur C. Clarke? That produced quite something. And the genius of the film is the ending does not violate the established laws of the universe presented in the film, but instead builds upon them.
Nolan and Shyamalan often violate their own laws for the sake of appearing "clever," but these are simply a wave of the magician's wand.