The past 12 months have delivered their fair share of changes on the ATP circuit.
Novak Djokovic may well have been able to retain his status as undisputed world number one, but Andy Murray finally managed to make his mark at the highest level by winning Olympic gold and claiming his first Grand Slam title at the US Open.
Rafael Nadal was forced to miss the entire second half of the season and, while Roger Federer enjoyed a great year, the Swiss and the Majorcan have been forced to accept Djokovic and Murray as genuine rivals.
Now the expression 'Big Four' - previously a questionable term, given the dominance of Roger and Rafa - is an entirely apt description of the quartet, as all four men are strong.
The year ahead, therefore, poses many questions which I will attempt to answer before the start of first real test of the new season, the Australian Open.
Can Murray continue his upward trajectory?
A player's ability to make major decisions often defines a career and Andy Murray must be congratulating himself on the one that tied Ivan Lendl to him about a year ago.
Since Lendl's appointment, many things have changed for Murray, with his gold medal and his first Grand Slam title.
The mix of counselling, chats that have resulted in mental breakthroughs, and real improvements in his game and working methods have finally enabled him to navigate those barriers which had so frustrated him previously.
These successes have triggered something powerful in him. As a contender he feels more legitimate, he seems prouder and therefore stronger. He has even started to hold his head higher and no longer seems ashamed to fall at the final hurdle.
All players, Murray included, see him as a potential winner at any Grand Slam now. All that remains is for him to fully control his character which still often plays tricks with him - at the ATP World Tour finals last year, he still appeared impatient and failed to seize his chance against Federer.
The Briton still lacks serenity and mental stability over the course of a long season, but there is no doubt he will continue to evolve in the right direction in 2013.
Can Nadal get back to the highest level?
It's a stark question, but a pertinent one. Remember that Nadal has been unable to pick up his racquet since his early exit from Wimbledon last summer. Hampered once more by the knee that has dogged him since the beginning of his career, he was unable to even perform the most modest of exercise for many months and was only able to return to court in November.
It will therefore be difficult for him to produce his best form during the first quarter of 2013. But he should be able to rediscover his game and become competitive towards April - the start of the clay court season, his preferred surface.
The only unknown is the severity of his injury, details of which are understandably kept secret. The Spaniard has relied on his body for many years. His qualities - spirit, determination, resistance to pain - are also his Achilles heel as they have pushed him to the limits, not least his body, which has come in for particular abuse.
All professional players are in a race against the clock, knowing their physical qualities and their ability to withstand the demands of top level tennis are related to their age. For Nadal, this perhaps rings even more true.
Is Federer on the brink of decline?
The question seems a little incongruous given that the Swiss recently returned to a level close to his best and was only a few victories away from ending the year as world number one.
But the question needs to be asked for two reasons.
First, because he is not getting any younger. Federer's playing style is based on a change of pace and an ability to be explosive, both of which are susceptible to the vagaries of time.
And secondly, because the gap between him and the other members of the top four has been reduced. Competition with the younger duo of Djokovic and Murray rages and if Rafa can rediscover his best form throughout the course of the year, the Swiss will have a lot to do.
Moreover, I saw at the ATP World Tour finals a Roger who was intimidated by an opponent for the first time (Rafa excepted). He started his semi-final against Murray in the worst possible way and even Roger said in his press conference after the match that he was thinking of his defeats to the Scot.
If Andy and Nole continue to progress this year, and with the return of Rafa, 2013 could prove to be a complicated year for the Swiss.
Can Djokovic maintain his supremacy?
The Serb started 2012 in the best of fashions by winning an epic Australian Open final against Nadal but then went on to have a first half of the season that was wracked with doubt.
However, he ended the year well and his number one ranking was deserved. Still he tasted defeat in 2012more than we had become used to.
His rival for the number one spot is now called Murray. The pair, both born in 1987, have comparable playing styles and are both baseline defenders.
While Murray has a more varied and powerful game, Djokovic retains a slight advantage in terms of mentality. 2013 promises to be important for both players, and their battles could well be decisive.