I recently started it and its definitely one of the most overlooked ones this generation... I'm enjoying it, though. There's not enough of this genre in FPS/third person shooters and its one of my favorites.
As for best PS3 shooters this gen, for me, its been Battlefield: Bad Company all the way... though I did enjoy Killzone 2 - "War. Perfected." was right. But CoJ is definitely among them. I'm glad I didn't pass up on it, even though it hit the bargain bin fairly quickly.