Don't get me wrong. I love most of his films, but His films all have a very similar tone and feel to them. In other words, you always know when you're watching a Nolan film.
I would argue that directors like Spielberg and Zemeckis are better because they can make films that are so different.
Spielberg can make raiders of the Lost ark, saving Private Ryan, and The terminal. All very different films, but all directed by the same guy.
Zemeckis made Back to the Future, romancing the Stone, and Forrest Gump. All three of those films are very differen.