It’s accepted wisdom in men’s tennis these days that the current generation of young players—starting with Rafael Nadal and Novak Djokovic, and on through the likes of Andy Murray and Richard Gasquet—is among the most diverse, dynamic, and stylish the game has seen in some time. Among this group of players in their early 20s, we find fantastic movers, power, finesse, and a few exciting personalities.

They are great to watch, no doubt. But it’s no longer too soon to worry about whether the potential of this crop of players will ever translate into meaningful victories or rivalries. For most of the String Generation, as Roger Federer has dubbed them, 2007 has not been a particularly impressive season.

Let’s take Nadal and Djokovic out of the equation for a moment. Set aside the 21-year-old Spaniard’s three consecutive French Open titles (he’s never lost at Roland Garros) and near dethroning of Federer at Wimbledon this year. Do the same for Djokovic’s first Grand Slam final and two major semifinals. Nadal and Djokovic are not up-and-coming players anymore. They have both arrived, and won’t leave the scene barring serious injury.

Nothing so assertive can be said of the remaining 15 men in the top 100 who have yet to celebrate a 23rd birthday. For a few of them, 2007 suggests that mediocrity or worse could burden them for years to come.

Marcos Baghdatis: After a dazzling 2006 (Australian Open final, Wimbledon semifinal, and a memorable evening with Andre Agassi at the U.S. Open) the Cypriot has stumbled badly this year. His ranking, at 11 this time last year, is now at 24. His play at the majors wasn’t awful (second round in Australia, fourth round at Roland Garros, quarterfinals at Wimbledon, and first round at the U.S. Open) but not much better than that. Baghdatis has some of the best strokes in the game and a wonderful sense of strategy, but his motivation is suspect. In Madrid last week, he looked out of shape, and he hasn’t played with confidence since Wimbledon of 2006.

Gael Monfils: The most talented athlete on the tour can’t seem to stay healthy, or perhaps more important, use his incredible speed and power for offense rather than defense. The idea of a 6-foot-4 player with a 145 mph serve who prefers to play 15-feet behind the baseline is, well, absurd. It hasn’t helped Monfils’ ranking much, either. He’s now at 40, compared to 33 at this time last year. Former pros and coaches rave about Monfils’ talent, but so far, it has mostly gone to waste.

Richard Gasquet: It seems as if Gasquet has been around for a decade, but he’s still under 23—and still something of an enigma. Few men have a better all-around game, and perhaps only one man, Federer, can pepper an opponent with winner after winner the way Gasquet did to Andy Roddick at Wimbledon this year, when he recovered from a two-set deficit for a place in his first Grand Slam semifinal. If that was one of the best performances of the season, then his second-round withdrawal at the U.S. Open—because of a cold—was one of the worst. If you can’t fight through a cold, how can you win major titles? Perhaps this is why Gasquet is a mere 5-21 against top 10 opponents in his career. Gasquet, currently ranked 11, was ranked 24 at this time last year.

Andy Murray: No one questions Murray’s talent. But will his body and mind allow him to develop it? If he can play most of next season without injuries, and with a lot less moping, Murray will give us a better sense of whether he’s in the class of Nadal and Djokovic or more like the rest. His ranking, 17, is the same as it was this time last year (16).

Tomas Berdych: In a generation that has many potential underachievers, Berdych could become the worst offender. Since he stunned Federer at the Olympics in 2004, the long-limbed Czech has done near nothing. Berdych can usually hide his slowness about the court with booming forehands and serves, but he can’t cover up his lack of toughness. There’s always a sense that a patient opponent will beat him, as Roddick showed at the U.S. Open this year (Berdych blew the first set and then, in rather pathetic fashion, retired with mild breathing difficulties). Berdych’s ranking has fallen to 13 from 10 at this time last year.

Sam Querrey: Not long ago, Querrey was steadily moving up the ladder to a career-high ranking of 47. He reached the third round of the Australian Open and defeated James Blake over the summer, but since then he has fallen to 61. One can only describe his last two months, in which he lost four of the five matches he played, as dismal: first round at the U.S. Open to Stefan Koubek, ranked 63; first round in Bangkok to Nick Lindahl, ranked 308; second round (after a bye) in Tokyo to Ivan Navarro, ranked 113; and second round in a challenger in Sacramento to Simon Stadler, ranked 220.

These six 21- and 22-year-olds are among the biggest names in tennis these days, and not one of them has been much better than mediocre this season. A few others in this class, however, have had better seasons without much recognition.

Take Dudi Sela, Israel’s top player. He defeated Fernando Gonzalez in Davis Cup last month and sent his country into the world group. Among the 22-and-under crowd, no one has jumped as many places in the rankings as Sela (from 285 at this time last year to 92). Jo-Wilfred Tsonga, who dueled with Baghdatis as a junior, has recovered from injuries and moved firmly inside the top 100 (65) for the first time in his career.

The two youngest in the group, 19-year-olds Juan Martin Del Potro and Ernests Gulbis, have had two of the best years. Del Potro is ranked 49, up from 93 last year; Gulbis, the hard-serving Latvian, has moved up to 47 from 204. This week he drubbed Thomas Johansson, 6-2, 6-1, in the first round of the St. Petersburg Open. Gulbis doesn’t have a refined game and isn’t as stylish as, say, Gasquet. But it’s wins that count in the end, and right now he seems to be learning how to do that more quickly than some of his young peers. Stay tuned until next year.

Tom Perrotta is a senior editor at Tennis magazine.