You can play PS3 ISOs and back up your own games internally or externally. Of course there's some games that are fucking huge and completely inconvenient to download though, FF13 is 40 gb. So, you might be better off buying the game. (Although I wouldn't recommend buying it or even dling it because it sucks.)
So, yeah. Right now I'm downloading Dead Rising 2 (5 gb. Almost done), I'll post and tell you whether it works or not.