What I liked about his reviews, is that he intentionally did not make them comprehensive. He saw his goal not to rehash all of the Apple Documentation (which you could read if you were interested), but rather to provide his opinionated perspective on what was interesting, and what spoke to the general theme of OS X's progression.
His reviews will be missed, but I agree, 15 years of stress/agony is more than enough for one man. He's leaving on the top of his game.
I hope a feature release will be of a similar caliber (i.e., "make ALL the things better") and I hope Siracusa is strong enough to stay away from it.