Well as far as I can see there is nothing significantly wrong with his game that I have seen lately. He is serving better than ever and as far as return of serve, one of the top three. At times it's almost annoying to see him attempt to retrieve a ball that you are sure he can not make and then he makes it into the other court for a point. He slides on a hard court as if it were clay and stretches into unbelieveable positions to hit the ball back to turn defense into offense. What do you have to do to beat this guy? I don't know and neither do most of the other ATP players. He does have bad days like everyone else but you better be playing at the top of your game even then.
Congratulations to Novak Djokovic winning the ATP World Tour Finals for three straight years and ending the year as number one again!