Top men's storylines for the Australian Open

The Australian Open is almost here. As part of our preview package for the year's first Grand Slam, Matt Cronin offers his top men's storylines headed in to the fortnight in Melbourne. For the top women's stories, click here.
Where does Roger Federer go from here?
Top-ranked Roger Federer has done just about everything. He broke Pete Sampras' record mark with his 15th Grand Slam title at Wimbledon, won the one major that eluded him at the French Open, finished at No. 1 in 2009 for the fifth year, got married and became the proud father of twins. Most analysts and fans are already calling the 28-year-old the greatest ever.
So what's left to motivate him at the Australian Open? Two things will get the Swiss pumped up: to avenge his painful and tearful five-set defeat to his archrival Rafael Nadal in the 2009 final and to show the young likes of Juan Martin Del Potro, who took him down at the U.S. Open, that's he not done yet.
Is Rafael Nadal back at the level where he can repeat as champion?
After he took two long and classic five-setters over Fernando Verdasco and Federer at last year's Australian Open, it looked like Nadal was prepared to dominate the rest of the season. After all, from June 2008 through January 2009, he won the French Open on clay, Wimbledon on grass, and the Olympic gold medal and Aussie Open on hardcourts. But then in the spring, the Spaniard's body began to break down and he hasn't won a title since early May.
Nadal looked a little more spry in reaching the Doha final at the beginning of this season than he did at the end of 2009, when he was clearly lacking in confidence. But in order to repeat as the Australian Open champion, he's going to have to play a lot more forcefully than he did at times late last year, because he can no longer count on his battered body to win a series of marathon contests.
Is Juan Martin Del Potro here to stay?
The young Argentine improved almost immeasurably from the start of 2009 (when Federer completely embarrassed him Down Under) to the latter part of the season (when he displayed guts, firepower and know-how in winning his first major at the U.S. Open).
Del Potro is the first man 6-foot-6 and over to win a Slam and he can hit through anyone on a great day, but the rest of the tour will be gunning for him now and he must show that he has heart and desire to stand tall in Melbourne and not wither like other young players have done in the past. If he can do so, he'll seriously threaten Federer for the top spot.
Del Potro suffered an injury Thursday at the Kooyong Classic and his status for the Australian Open is uncertain. Hopefully he'll be at full strength for another run at a Slam title.
Will Andy Murray finally break through?
The fifth-ranked Scot appears to have all the tools to win his first Grand Slam: intelligence, variety, much-improved conditioning and weapons all over the place. But he was largely ineffective in closing out big matches at the majors last year, often playing too passively and failing to come up with the goods at critical junctures.
Britain has been largely patient watching the 22-year-old progress and he's been outstanding outside of the majors, but if he doesn't snag a Slam title this year, the comparisons to another talented British player who never won a major title — Tim Henman — will come sooner than later.
Is Nikolay Davydenko for real?
The cagey Russian veteran has been the biggest surprise of anyone during the past three months, beating Federer and Nadal both at the ATP World Tour Finals and in Doha to win the titles. He's quick, deceptively powerful and knows how to change the pace to his liking.
But even Davydenko isn't sure whether he can win his first major, as the slight and sometimes brittle Russian isn't sure whether he can wear down his foes in best-of-five-set matches. Clearly, he's found himself, but when the world is actually expecting him to deliver, will he be able to maintain his composure and hit his spots? His recent history says yes, but his overall history says no.