Even though the 650 sounds like it won't be much worse than a GTX660, it is. Its a lot less powerful. Combine that with running at retina resolution and your going to have to turn graphics settings to low in order to play any modern game at 30fps or higher.
I just find it funny how many people get so defensive over an Apple product. I myself really enjoy my macbook air, Imac and iPhone but I couldn't see spending 3 grand on a mediocre laptop. OMG its got an aluminum case and I use it for work, yet the first thing I do when I get home is see how it can game and then tell other people about gaming on it.