There are numerous reason why I want to the Nexus 5X. First and foremost (for me) is pure, unadulterated Android. Google's Android. I can add any features I like from the OEM's devices with an app
Updates... specifically the speed of updates.
Almost every site has been raving about the speed of the fingerprint sensor. I can't wait to give it a try.
The size, I think, is just about perfect. The ability to use it one-handed is fantastic.
I could go on, but it would take all day.