He is widely considered to be one of the best directors of all time. He only filmed 13 movies in his 46 year career, but they're all considered masterpieces and are the best of their genre. Films like 2001: A Space Odyssey and A Clockwork Orange are frequently discussed as being some of the best movies of all time.
His works are timeless, but they weren't recognized by the peers of his time. While his movies were nominated for multiple awards, the only Oscar he ever won was for 2001: A Space Odyssey. The category? Special Effects.