Aside from having to adjust to a new user interface and different input methods (which has gone pretty smoothly, in all honesty), it's been great. I'm mostly using its built-in features/applications for now while I figure it out and assess how they impact battery life. Siri, texting, phone calls, activity tracking, and I gave Passbook a try at Starbucks today.
I've added a few third-party apps, such as Calcbot and Workflow, but I haven't done much with them yet. I kinda want to wait until developers start getting a handle on the way their Watch apps/extensions should work before I start going nuts with the apps.
Slow and steady, right?