I find it nice for all the stuff I usually fish out my phone for, except now I don't have to do that. I use the custom face, so I've got temperature, my exercise goals, all that jazz on it. Got it synced to my home & work calendars too, so I always see my next appointment.
The killer app for me is basically Siri. I use it all the time to look things up, get directions, and set timers/alarms (I do a lot of craft/prop building, which means timing glue and paint). Haven't really had too much trouble with battery life: I put it on around 7ish, take it off about midnight, usually got >30% juice left, usually closer to 40%. Occasionally use the Wallet app, but not on any sort of regular basis.
Things I don't like: Siri doesn't always come when I call. The history feature is more in the way than anything, and the screen doesn't fire up every time I turn my wrist like ti's suposta. I tend to wiggle it a couple times, then give up and just tap the screen
Still, I like it for the most part. Still use it every day. It makes a nice sort of 80/20 remote terminal for my phone, if you see what I mean. For that, it does a good job.