I don't care about apps or watch faces or any of that stuff.. I use it for (1) notifications and (2) the calendar timeline..
Being able to glance at my wrist when I get an email or a phone call (or any notification) without having to fish my phone out of my pocket, especially in the winter when it's deep inside my coat, is invaluable.. I can quickly decide "do I need to deal with this right now" (which for me, during the work day, is important).
Being able to tap the down button and see the next thing in my calendar (or the thing after that, etc) is also super useful.
For me personally, that's the killer app, and it's why I am so sad that Pebble is gone, because their calendar timeline was innovative and super useful (to me at least), and combined with quickly checking notifications, made my Pebble Time as essential as my wallet when leaving the house.
Also, it looks great.. Better than any other smart watch that provides the same functionality.. And the battery lasts for a week..
Ok I'm going to stop, because now I'm just bumming myself out that my Time Steel 2 will never arrive.. :-(