The killer app was driving with the Apple Watch (not what I would have expected). I found the GPS vibrating prompts, a glance at the watch for next turn really awesome features and I try not to drive anywhere unfamiliar without it. This is one area that's super subtle but really well thought out.
Again useful during driving, I also found the ability to skip music with my hands still on the steering wheel to be incredibly helpful. Feels safer than taking my eyes off the road to fumble my phone.
Would I pay for the next Apple Watch? Maybe. But I definitely no longer consider myself an Apple Watch hater.