I imagine a lot of this will be decided by the success or failure of the online-pass model. I only just started trying Gamefly, but already, the vast majority of games I'd like to try require the purchase of an online pass to be able to fully appreciate the game. Even with something like NFS:The Run, where I don't particularly care about racing online, many of the vehicles can only be unlocked by doing online races. Same with SSX, need online pass. For that one, I'll probably just wait till fall when it's down to $20 anyway, then buy it new. I'm not sure how long I'll stick with Gamefly, as unfortunately, I already have most of the current SP heavy-hitters, AC 1,2, etc. UC 1,2,3, Batman AA and AC, etc. I could see it being great for a new PS3 owner though.
Enjoying BF4 on the PS4, bugs and all.