I thought I'd check Metacritic to get a decent comparison of Xbox 360 vs. PS3 instead of PS3 (2007) vs. PS3 (2008).
Here's what I found: the PS3 has 9 games with an aggregate score of 90%+ and only two are exclusives. The Xbox 360 has 17 games with a score of 90%+ and six of which are exclusives.
The trend is similar for games rated between 80% and 90%. Careful study of the multi-platform titles show higher scores for the Xbox 360 version most of the time: Bioshock, Fallout 3, NHL 09, Dead Space, Rock Band 2, and more. Although not multi-platform, in the battle of recent big FPS releases, Resistance 2 is badly outscored by GOW 2 (94 -88).
I shake my head when PS3 owners are still trying to convince themselves that they have just as many (or more) great games to chose from.