I like that it's pre-vetted hardware for running Ubuntu/Linux, has very long battery life, and the screen is really a joy to look at.
It's a 13-inch screen crammed into an 11-inch laptop body, so you get a lot of screen real-estated without the full bulkiness.
I also love the lightweight (close to MacBook light here), and the versatility in connectors (a detractor for the MacBook line for me).
In addition, out of the box things like 5GHz ac wifi just works under Linux.