The 2013 PGA Tour season had four different major winners and 31 different regular event winners. Tiger Woods added five victories to bring his career total to 79, three short of Sam Snead's record of 82.

Phil Mickelson finally broke through in the Open Championship, the one event he seriously doubted he would ever win. A 19-year-old kid from Texas, Jordan Spieth, became a full-fledged superstar in one year, giving us perhaps the best season by a rookie since Tiger Woods in 1996.

By late summer, Henrik Stenson was the best player in the world.

So far in 2013, former world No. 1 Rory McIlroy has yet to earn a victory anywhere in the world. Although the Northern Irishman disputes it, among the many issues cited by critics for his woes this year was his complete changeover to Nike equipment. Streeter Lecka/Getty Images

Jack Nicklaus was right last week when he said that we have as many good players as we have ever had in the game. This season was a testament to that assertion.

Yet the year also left me with some lingering questions. Here are five I'll be mulling for the next few months.

1. Rory McIlroy's audible

The most baffling aspect of McIlroy's 2013 season isn't that he made wholesale changes to his golf equipment after rising to No. 1 in the world ranking a year ago. It's hard to scold him for taking Nike's money and joining the global sports marketing machine.

What's more disconcerting is how a player of his caliber couldn't adequately adjust to the new gear and the heightened pressure to win at least one worldwide event, or show consistent flashes of the brilliance that led him to 8-shot wins in two majors.

It's one thing to not win but still have several top finishes, but McIlroy didn't even make the Tour Championship.

Will he ever be as good as he was in 2012, when he won five times worldwide? Can he again separate himself from the game's elite in much the way Tiger has over his career? What will the 24-year-old Northern Irishman do to right his way in what has still been a very brief career?

He has the remainder of 2013 and next year to answer these questions.

What's unmistakable is that his confidence has taken a major hit in the past 10 months and that he has a lot of work to do to regain his place as the No. 1-ranked player in the world.

2. Major headaches for Tiger

For nearly 20 years, Tiger Woods' name has been synonymous with major championships. From that first historic Masters win in 1997 to his heroic victory at the U.S. Open in 2008, Woods has done perhaps more than even Jack Nicklaus to raise the public's fascination with the big four.