Were you downloading other things with the R&C demo? PS3s only download one thing at a time, so...
Ninja Gaiden Sigma?
Virtua Fighter 5?
Heavenly Sword is a pretty awesome game. I don't regret buying it, but I *hate* renting games.
I was going to suggest R&C at the top of the list, but other guys beat me to it.
That being said, DMC4 *and* Turok come out on the 5th, so you might want to wait a few days.
I know I'm getting Warhawk and DMC4 at the same time, but I'll sit out Turok. I love dinosaurs, hate FPS, and the demo on their site was a lot more 'generic FPS' than 'DINOSAURS!' Not surprised, but am disappointed.