Having a Nexus 5, that made me jump from the iPhone guys over to Android, with it's awesome Kitkat and great specs with an amazing price, I love the new Nexus 5X because it fixes some of the few issues on the original 5 that matter the most to me: the short battery life (for my usage case) and the lack of fast charging.
Being an IT guy and using my smartphone all day long for work (Sysadmin stuff - SSH, Nagios monitoring, Notifications over Pushbullet, VPN, mobile hotspot, google drive and ms onenote for portable documentation, hangouts for work messaging, skype for video calling and yes, the flashlight, for going on some dark places to fix network problems) and fun (reading Android Central, listening Podcasts to learn new stuff and catch the latest tech news, spotify on the car over bluetooth, netflix, youtube), the fast charging is for me the best feature of the 5X and the one that I care the most because it means that I can finally leave my portable USB charger at home with confidence. With my Nexus 5, I need to recharge at noon... :-(
Other than that, the other new features like the fingerprint sensor and the improved camera (altough I like the 5 camera) are also very nice, along with the USB-C (I can finally be on par with my wife over her iPhone's cable charger
)
Google made a solid upgrade to a phone that will be a forever remembered, I think.