Serena Williams has been dominant yet only won two of the four grand slam tournaments on offer. Not a bad return, but for a player who goes into next week's season finale, the WTA Championships in Istanbul, with a 73-4 win-loss record, it is perhaps something of an underachievement.
Some have claimed that Williams' dominance is making women's tennis boring. At her best, Williams is unbeatable. She has a realistic claim to the title of greatest woman tennis player ever; only Steffi Graf and Martina Navratilova present any challenge for this honour.
But it is not Williams who is making women's tennis boring; it is the dearth of meaningful rivalries which is causing the dissatisfaction. Williams is world No.1 by a country mile, having amassed a lead of more than 5000 points in the rankings between herself and Victoria Azarenka. The world No.2 has inflicted two of Williams' defeats this year yet she still remains unable to do it when it really matters - in the grand slams - as both of the Belarusian's victories were in WTA Tour events. Still, it is the closest thing to a rivalry in women's tennis at present.
Maria Sharapova will miss the WTA Championships next week due to an ongoing shoulder injury, despite qualifying in third position. The Russian seems the most obvious contender to be Williams' rival. They both transcend their sport and are the only two active players who hold the career grand slam. However, to suggest a rivalry exists between the pair is an exaggeration.
Williams' and Sharapova's career head-to-head record is 14-2 in favour of the American. The Russian has not beaten Williams since 2004, and has only won one set since 2008. Sharapova has admitted that to call her and Williams rivals is somewhat disingenuous, saying "it's not really a rivalry until I win a few more matches". This may be out of character for her, but it is certainly true. Despite Sharapova's resume paling in comparison to Williams', she is the highest paid female athlete in the world. Williams appears to dislike the attention which is lavished upon Sharapova and relishes putting her in her place on court. These almost sadistic demolitions show no signs of abating in the coming season.
Another shortfall in the women's game at present is the lack of strength in depth of players in the 6-12th positions in the world rankings. This is highlighted by the fact that, on the men's side, the depth of talent is a strong point. Players such as Jo-Wilfried Tsonga, Tomas Berdych, Stanislas Wawrinka and, more recently, Roger Federer occupy these spots, while the women have the likes Sara Errani, Angelique Kerber and Roberta Vinci, who most of the general public would struggle to identify if their life depended on it.
These lack of meaningful rivalries may be a drawback, but the situation also presents a real opportunity for younger players on the WTA Tour; Laura Robson being a prime candidate. Robson is ranked 46, having been at a high of 27th earlier this year. Her career to date has included several high-profile scalps of top-10 players, but she has displayed a chronic inconsistency which so often characterises young players' performances.
Robson is just one of a crop of teenagers who have broken into the world's top 50 over the past year or so. Compatriot Heather Watson, Madison Keys, Eugenie Bouchard and Elina Svitolina have all made an impact on the women's tour this season.
Perhaps the most exciting development in 2013, however, has been the emergence of the 20-year-old American, Sloane Stephens. She missed out on a place in the WTA Championships by just two spots. Stephens and Williams are developing a nascent rivalry which may develop into the most intriguing match-up on the Tour in 2014. Stephens beat Williams in the Australian Open quarter-finals in January - the first time that Williams had ever lost to a younger American. The pair began the year professing to be best of friends but, after Stephens' victory, that friendship was quickly curtailed, with the pair claiming to be Fed Cup team-mates and nothing more.
While friendship does not necessarily extinguish any hope of an on-court rivalry, a touch of animosity does no harm. It harks back to the days of Williams' oppugnant relationships with Justine Henin and Martina Hingis - and just adds a little spice.
But the Williams-Stephens rivalry will have to wait until 2014, if it transpires at all. Next week at the WTA Championships, if Williams brings anything close to her best performance, she will win. Azarenka will most likely pose the greatest challenge but we may have to wait a while yet until the women's game is as competitive as the men's.