Apparently is ranked as the second best pitched game, only behind Kerry Wood's 1 hit, 20 Ks and tied with Koufax's perfect game with 14 Ks.
http://espn.go.com/blog/sweetspot/post/_/id/25634/did-matt-cain-throw-greatest-game-ever
I assume that's based on "game score" and therefore the only things that count are the number of strikeouts (other inputs are hits, walks, & runs, of which there were none). I don't know that there is any quantifiable way to say how good a pitcher's stuff was in any particular game, per se. I watched the MLB highlight that showed all 27 outs and there were at least 2, maybe 3 strikeouts on called third strikes that were debatable and at least 3 balls that were smoked, but hit right at defenders. I think one of the called third strikes was on a full count, too, so if the call goes the other way, no perfect game.
I can't say how that compares to any other perfect game, though. He did throw like 125 pitches and 85 strikes. It would certainly be an interesting study to compare at least those perfect games where you could get video for a comparison.
