The franchise cornerstone isn't having one of his best years offensively, but still is the biggest threat in Tampa's lineup. He's posting All-Star type numbers, batting .270/.348/.506 with 25 homers, 66 RBI and a 135 wRC+ (Weighted Runs Created Plus).
The only Ray with a higher wRC+ right now is Wil Myers, who stands at 136 wRC+. Longo does, however, lead the team in home runs, RBI, slugging percentage and ISO (Isolated Power).
Where Longoria really stands out from the rest of the team is in his WAR, which at 5.7 is actually the fourth highest in the American League. In terms of WAR, no Rays player has been really close to being as valuable as Longoria this year with Yunel Escobar (3.6) and All-Star Ben Zobrist (3.5) the next-closest.
Longoria's extraordinary defense has been a huge part of his value this season and throughout his entire career.
Having another Gold Glove-caliber year at the hot corner, Longoria owns an outstanding 14.6 UZR (Ultimate Zone Rating), which is third-highest among AL fielders, a .973 fielding percentage (second-best among AL third basemen) and 11 DRS (Defensive Runs Saved).
It's pretty clear that Longoria is the Rays' most valuable player, and his long absence in 2012—in addition to his statistics—serve as proof for that.
Having him healthy in the Tampa Bay lineup has been one of the main reasons for both the Rays' improved defense and offense this season.
All stats according to FanGraphs.com.