Yes, he's a class act, a first-ballot Hall of Famer, and the best modern closer ever. But two little nits:
First, there's a meme that says "More people have walked on the moon -- 12 -- than have scored in the postseason against Mariano Rivera." Close, but no. True enough about the 12 on the moon. But Rivera's allowed 13 postseason runs: Marquis Grissom in 1996; Sandy Alomar in 1997; John Olerud, Benny Agbayani, and Jay Payton in 2000; Johnny Damon, Ichiro Suziuki, Midre Cummings, and Jay Bell in 2001; Todd Walker in 2003; Dave Roberts in 2004; Vlad Guerrero, in 2005; Chone Figgins in 2009. I suppose 13 runs over 96 games isn't all that shabby.
Second, consider the following two pitchers:
ERA IP H BB K W L
Pitcher A 5.94 50.0 64 20 38 3 3
Pitcher B 5.70 53.2 75 18 36 2 5
Pretty similar, right? Well, Pitcher B is Jamie Moyer last year - end of the line, age 49, playing in Colorado. Pitcher A is Mariano Rivera as a starter. The point being: It's a lot harder to start than it is to relieve. Rivera started only in 1995, when he was 25, and he probably would've gotten better. But he certainly wouldn't have posted the 2.06 ERA as a starter than he did as a reliever. Again, he's an all-time great, but he's an all-time great in a lesser role than that of a starter.