Eh, I find Nolan mediocre. He may be your favourite director, but does he deserve to be ranked alongside Chaplin, Bunuel, Tarkovsky, Lynch, Kubrick, Welles, Scorsese, Kurosawa, Ozu, Wilder, or Keaton? Hell no.
And that is exactly what you asked.
Anyway, he ranks among the greatest of all time. Look at the movies he did :
-The Dark Knight
-The Dark Knight Rises
The last 2 maybe not quite at the same level as the others, and Memento is one of the greatest movies of all time. Seriously under-rated.