Renting via Gamefly was great throughout the past year. I had to cancel it recently though, but I'd like to use it again. Sometimes you couldn't get access to the games you wanted on your list based on their supply and you'd have to wait around 4-5 days once you send out your game for a new one to arrive, but I was also able to play through great games like ICO, Zone of Enders 2, and Okami and a lot of other good/decent/crappy games this way.
I'd say it all depends on how good the game is, it's length, and how much replay value there is.
In the case of Mirror's Edge for example, I beat the game in one day and I only had enough interest left in trying to get a couple of trophies before I sent the game back the next day. Well worth avoiding the $60 price tag.










