First, the fact that its "E-paper" display is always on means it works well as an old-fashioned watch so I can instantly tell the time. (I still find it crazy that the Apple Watch display is off by default!)
Pebble's notification support works really well with Android so I can see at a glance whether a new email or WhatsApp message is something I need to respond to on my phone. Most of the time I don't, so I spend less time fiddling with my phone.
The feature that I most appreciate that I hadn't anticipated is that the Pebble vibrates and shows who's calling when someone calls me. Which means I can keep my phone on silent all the time but never miss a phone call.
So I'm definitely a fan of the Pebble Time. Its UI is really simple and well thought out, especially compared to the Apple Watch, and there's really nothing else I need it to do, apart perhaps from being more physically attractive.