This is a phenomenal shoe. And I am by no means an expert, but the Flyknit Racer might be the lightest shoe I've ever worn. The fit is also fantastic - Nikes tend to run a little small and narrow but I had no problems ordering at Nike.com. If fit is a concern, however, it would be wise to go to a Nike outlet and get a proper measurement.
The cushion on these things is also fantastic, especially relative to how almost-non-existent the weight is. Again, the real "game changer" here is the weight of these great running shoes. Easily worth trying on if you have any interest in running. How they hold up under extreme conditions is anyone's guess. But out of the box? An amazing and durable shoe.