There have been many surprise players this year in the NBA. Which players, according to advanced stats, are the most improved from a season ago?

The NBA is just like anything in life â€“- things recycle, players get older, and new players replace them. Our favorite players growing up -- like Michael Jordan, Charles Barkley, Larry Bird -- all eventually retire and make way for the new generations.

I know some people get sad or nostalgic about that cycle, but I personally find it exciting. Who knows whatâ€™s out there â€“- until last year, we thought LeBron James will easily be the best player of our generation. Then comes Anthony Davis barging onto the scene. Who knows anymore what could happen?

Thatâ€™s the beauty of the NBA â€“- thereâ€™s always something different and something new. We constantly have players changing the â€œprototypeâ€ of what a player or position should be. Both Russell Westbrook and Stephen Curry are superduperduperstars, yet they play completely different brands of basketball. Is one way â€œcorrectâ€? No, of course not. There is always space in the NBA for all types of players.

So who are the players barging onto the scene this year?

To gauge this, I looked at some statistics, specifically VORP (Value Over Replacement Player) and WAR (Wins Above Replacement), calculated from ESPNâ€™s Real Plus-Minus.

Warning: some of the breakout players might surprise you.

Letâ€™s start with VORP. Hereâ€™s a list of the top-20 players (actually, a couple more than that because of ties at the end) in terms of this yearâ€™s VORP minus last yearâ€™s mark. It will give us a picture of which players are making a leap into better play this season.

Note: Data as of 2/23/15

Value Over Replacement Player

Player '13-'14 VORP '14-'15 VORP Difference Rudy Gobert -0.2 2.4 +2.6 Al Horford 1.0 2.6 +1.6 Tyson Chandler 1.3 2.9 +1.6 Rodney Stuckey -1.0 0.6 +1.6 Gorgui Dieng 0.5 2.0 +1.5 Russell Westbrook 3.1 4.6 +1.5 Ed Davis 0.2 1.6 +1.4 Khris Middleton 0.2 1.5 +1.3 Pau Gasol 1.1 2.4 +1.3 Jeff Teague 0.7 1.9 +1.2 Brandon Knight 0.7 1.8 +1.1 Lavoy Allen -0.2 0.9 +1.1 Tony Wroten -1.0 0.1 +1.1 Lou Williams 0.1 1.2 +1.1 Giannis Antetokounmpo 0.1 1.2 +1.1 Donatas Motiejunas -0.3 0.7 +1.0 Evan Turner -1.0 0.0 +1.0 Patrick Patterson 1.3 2.3 +1.0 Marc Gasol 2.3 3.2 +0.9 Ben McLemore -0.5 0.4 +0.9 Harrison Barnes 0.4 1.3 +0.9 Devin Harris 0.1 1.0 +0.9 Alex Len -0.3 0.6 +0.9 O.J. Mayo -0.6 0.3 +0.9

The lanky Frenchman, Rudy Gobert, dubbed â€œStifle Towerâ€ for his shot-blocking prowess, is having quite a year in Utah â€“- enough so that the Jazz felt comfortable moving young center Enes Kanter at the trade deadline last week. He kind of came out of nowhere, as he was the 27th-overall pick in the 2013 draft and was taken as a high-upside project that may or may not work out.

You could say heâ€™s working out. According to Nylon Calculus' rim protection statistics, Gobert is easily the best rim protector in the league. He saves approximately 4.38 points per 36 minutes for the Jazz, which is miles ahead of second-place rim protector Hassan Whiteside (who, by the way, is pretty much a shoo-in for this article next year). The Jazz have a great future in Gobert, newly re-signed Gordon Hayward (who youâ€™ll see on the WAR list), Derrick Favors, Alec Burks, and Dante Exum.

Itâ€™s nice to see some veterans bounce back from either subpar seasons or injury-filled ones -â€“ Al Horford, Tyson Chandler, Pau Gasol, and Marc Gasol have all been great, important pieces for their respective teams this season. There has been a lot of talk about the Hawksâ€™ jump into contender status, and Horford deserves a lot of the praise. His play on both ends of the court has been key to putting teammates Kyle Korver, Paul Millsap, and Jeff Teague (also on this list for good reason) in situations where they can succeed.

Itâ€™s interesting to see Brandon Knight on this list, as he was just flipped to the Phoenix Suns by the Bucks for another point guard, Michael Carter-Williams. Knight is having a fantastic season this year â€“- heâ€™s at 17.7 points, 4.1 rebounds, 5.4 assists, and 1.6 steals per game, not to mention 40.4% from the three-point line. And, oh yeah, heâ€™s actually a couple months younger than NBA sophomore Carter-Williams. Heâ€™ll get paid this summer, and he deserves it.

Wins Above Replacement

Player '13-'14 WAR '14-'15 WAR (Estimated) Difference (Estimated) Kyrie Irving 1.45 13.12 +11.67 Khris Middleton 0.10 11.14 +11.04 James Harden 9.67 19.74 +10.07 Tyreke Evans -0.75 8.96 +9.71 Anthony Davis 5.46 14.18 +8.72 Ben McLemore -4.29 4.10 +8.39 Markieff Morris 3.20 10.81 +7.61 Lou Williams 0.28 7.48 +7.20 Darren Collison 0.82 7.84 +7.02 Cody Zeller 0.09 7.08 +6.99 Jeff Teague 2.05 8.96 +6.91 Gordon Hayward 4.99 11.72 +6.73 John Wall 8.30 14.55 +6.25 Tyson Chandler 5.80 11.99 +6.19 Brandon Jennings -2.82 3.29 +6.11 Russell Westbrook 6.89 12.94 +6.05 DeMarcus Cousins 4.45 10.47 +6.02 Draymond Green 6.54 12.17 +5.63 Harrison Barnes -0.74 4.64 +5.38 Jared Dudley 1.93 7.26 +5.33

WAR is cumulative, so itâ€™s not a strict comparison like VORP until we estimate each playerâ€™s end-of-season WAR. To (very roughly) do this, I took the pace each player was on, accounted for injuries and games played, and estimated what their WAR would be at the end of the year. Itâ€™s not an exact science, but provides a nice talking point next to VORP to judge players.

Kyrie Irving with the top spot! That was a bit of a shock and really shows how having help â€“- especially when your help is in the form of LeBron James -â€“ can really elevate a player. Itâ€™s really hard to explain the jump with Irving because itâ€™s so massive. He essentially went from statistically an average guard in the league to a superstar in a single year. Iâ€™ve been bearish on Irving for the early part of his career, but that is changing this season. Itâ€™s amazing what good teammates and motivation can do.

And just when you thought you were shocked with Irving, we have Bucks' wing Khris Middleton in the second spot! Looking at Middletonâ€™s per-game stats, you might be wondering how heâ€™s so high on the list. After all, his per-game averages of points (11.7), rebounds (4.4), and assists (1.9) are right where they were last year, if not a little below. So what gives?

With RPM, defense is heavily factored into the equation, and weâ€™re learning a lot as a basketball community just how important defense is to a team. Middleton is statistically as good as it gets when it comes to defense â€“- among all shooting guards, he ranks number one in the NBA in Defensive RPM (DRPM) at 4.10. Heâ€™s ahead of noted defenders Andre Roberson, Danny Green, Andre Iguodala, DeMar DeRozan, Wesley Matthews, and Klay Thompson.

Middleton is also shooting a ridiculous 41.8% from the three-point line. Itâ€™s probably fair to say he is the best 3-and-D guy in the league right now. Heâ€™s making less than $1 million this year as well, making him potentially one of the most valuable players in the NBA this season, if you judge in terms of dollar-per-whatever-production-statistic you'd like.

Also on the list are obvious guys like James Harden and Anthony Davis (both having MVP-type seasons), Ben McLemore (bouncing back from a bad rookie campaign), Markieff Morris (making his new contract look ridiculously valuable), Gordon Hayward (ditto), Lou Williams (sixth man of the year?), Cody Zeller (a bright spot for Charlotte), and Draymond Green (gonna get paid this summer). There are so many good storylines this year and so many exciting, great young players to watch. The NBA has such a deep talent pool and is certainly setup to be outstanding for a long time. Letâ€™s enjoy it.