This is a new 2017 model running Android Wear 2.0 OS.
It has built-in GPS, 50m water resistance (swimming, basically), and a lot of sensors...
You can interact with it with your voice ("OK, google").
It's compatible with Android devices running Android 4.3+ and iPhones running iOS 8.2+, though functionality with iPhones is a bit limited.
Battery is said to last for up to 25 hours, and there's a charging port on the side.