His save total was only 6th highest, but he had his lowest ERA, WHIP, highest ERA+, and best K/BB ratio in his 14 years in the Major Leagues. He only walked SIX batters in SEVENTY AND TWO THIRDS INNINGS while striking out seventy seven. 12.8 would be a sick K/9 ratio, but that was his K/BB ratio. (his K/9 was actually slightly lower at 9.8). Frankie Rodriguez might have tallied 62 saves and overshadowed Mo, but his WHIP and K/BB ratios were significantly worse than Rivera's worst season. Which was 2007.
Rivera and Jorge Posada both signed massive contracts (especially compared to the ones being signed this offseason) last year at the ages of 37 and 35, respectively. The older of the two men had his most valuable season as a Yankee, while the younger chap has his least. Both had shoulder surgery over the offseason performed by Mets' doctor David Altchek, but Jorge's was far more serious. Mo had some calcification removed from this right shoulder joint, while Posada's procedure was to repair his glenoid labrum.
Mo is a completely unique case. There is no precedent set for a 39 year old (predominantly) one pitch reliever who just posted his worst and best seasons as a professional back to back. Statistically, relievers are much more prone to sharp declines because one three run homer (like Marco Scutaro's dinger off the foul pole in Oakland in 2007) in a 70 inning season takes an ERA from 1.80 to 2.19. A couple bad outings and you are looking a drastically worsened statistical profile.
Am I worried about Mo? Yeah, a little bit. Although it was a minor surgery, he still went under the knife. Rivera is such a finely tuned man-chine you get the feeling that he could make the necessary adjustments. He is ubiqutously revered by Yankees fans and feared by those of opposing teams. He's been so good for so long that it's easy to take him for granted, but some point he is going to enter a decline phase.
For the heck of it, here is my prediction (barring injury):
72IP, 2.25 ERA, 67K, 13BB, .975WHIP