For me, its all about unibody. Screen quality. Trackpad touch and feel. Keyboard comfort. The rMBP fits the bill for all of these things - I'm NOT content with OSX as an operating system, however, this is just something I put up with (and since I run my Linux dev environment in a VM, big deal anyway). I'm certainly not a typical Mac user - I spend 99% of the time in the terminal.
I've looked at the Google Pixel series, and some of those look like they come pretty close - except I have no desire to use a Google operating system, of course .. and they're just not available locally, like the rMBP's are. But if there were a manufacturer who puts together a machine that has the physical characteristics of the rMBP, I'd happily abandon Apple hardware in an instant.