I like my Apple Watch (the Sport - read "inexpensive" - model). I like having notifications on my wrist, because it's a lot less disruptive to make a quick glance at my arm than to pull out my phone. Don't underestimate the convenience of seeing your next scheduled appointment at a glance! I also really enjoy the activity tracking. I used to have a Jawbone UP but I had to send it back several times for repairs; it wasn't up to the rigors of my Desktop Warrior lifestyle. My watch (plus a couple of third-party apps) is far more useful for fitness stuff than the UP ever was.
watchOS 2 went a long way toward converting the watch from a fun gadget into something genuinely useful, and by all accounts watchOS 3 sounds like a huge step forward. If I lost my phone, I'd hightail it to the store to pick up another one ASAP. It's where I keep my schedule, to-do list, contacts, and other stuff that makes day-to-day life as easy as possible. If I lost my watch, I'd meander back to the store when I had some free time. I'd be bummed and would keep glancing at my naked wrist out of habit, but I'd survive. I would eventually replace it, though. While I could certainly live without it, I like having one and wouldn't voluntarily go without.