The fact that I can wake up with out waking up my other two house mates is great. The watch taps me gently and increases until I start moving around, to which it then fades away and if I don't move again for a few minutes it comes back. It's a really gentle and effective way of nudging you awake without getting in the habit of hitting snooze.
The watch and app graphics are nice and dark. I point this out because too many sleep apps are way too bright.
I can start the alarm from my watch, my phone can be plugged in and away.
I would like to see some refinements in the app UI. There are a lot of great features but they're hidden behind strange buttons and tucked away deep within menus. A walk-through wizard to set up the alarm and an easy to update dashboard when you first get to the app would be amazing.