Novak Djokovic ended the year as world number one and that in itself is a great achievement.
This year, there was no one player who was able to dominate the circuit as Djokovic did in 2011. All four Grand Slam titles were shared by different players. And the battle for world number one status raged between the Serb and Roger Federer right until the end.
Djokovic was far less dominant than he had been in 2011, but he still managed to bounce back from the period following the Australian Open, when he couldn't seem to string victories together.
The end of the first part of the year was very average for him, notably at Roland Garros where he seemed to lack confidence from the early stages right to the final.
The second part of the season was better, despite his failure to claim another Grand Slam title. He was consistently in the mix and managed to finish well by winning the ATP Tour Finals in London, even if that tournament is less intense than the Majors.
Djokovic experienced several mental phases over the course of the season. I think that his status as undisputed number one in the world was a little hard for him to handle. After the Australian Open, he became aware of just what he had achieved and that shook his confidence a little.
That showed he isn't a complete player, rather a player who reacts to his mental state. His game falls apart when he is suffering from a lack of confidence.
He has fewer weapons in his armoury than Federer or Andy Murray, and consequently he finds it more difficult to get himself out of these delicate situations. He cannot allow himself these moments of doubt; if he does, his game suffers a great deal.
Djokovic's end of season was rather encouraging for the coming year, although I don't think he will ever be able to reproduce the level of confidence he reached in 2011. That season will remain an exceptional year for him.