From what I've heard from other people, your experience with gamefly will hinge a lot on your location. If you're near a distribution center, you'll get things quick. Otherwise, you might be left waiting awhile. I've been told the Midwest is the worst region to live in in that regard.
They also have supply problems. Supposedly, if you just keep one or two games in your queue, they'll be forced to send you those. If you compile a list of 20 games, they'll send you all the old ones and you won't ever get a new release.
Take a free trial and see how it goes.