Djokovic has a great style which may not be aesthetically pleasing but is extremely effective in beating anybody on any surface.
He doesn't have any real weakness anymore. The only way to beat him is to play god-level and have tremendous variety and even then it's going to be tough.
I can't wait to see more Nadal/Djokovic matches this season on clay. Djokovic is stronger than last year. Seems like he's back into his 2011 mode or close to it. Bigger serve, bigger forehand.