A few months after launch I snagged one on sale for $175 and I quite enjoy it (although not necessarily for the reasons I originally expected to).
My experience: it's nothing groundbreaking like your first (or latest) smartphone because it's largely just an extension of that smartphone. I don't really run too many watch-specific applications and mostly use it for quick notifications/replies and the occasional case where having a control on my wrist is nicer than messing with my phone.
One example of that would be navigation while riding my motorcycle. I don't have a phone charger/mount but I can fire up nav before leaving and glance down at my watch to see upcoming turns. It can also be nice as a remote for my phone's camera or to pause something I'm casting to the TV like a Netflix show.
Honestly my main, favorite thing about this watch is the ability to change the face to look like just about anything I want. I never would've guessed this at first but this is my stupidly obvious killer app (or at least the most enjoyable). There are several great watch faces for free or cheap on the Play Store and thousands of them available for download and application through apps like Watchmaker.
The fact that this is just a programmable screen means you can make it look like a subtle, classy "traditional" watch or you can do things not possible on traditional jewelry. If I felt like it I could swap between a long list of favorites to match whatever I'm doing or even what I'm wearing. Granted I'm not quite that obsessed with fashion or anything but it's a surprisingly cool thing to have.
And since I enjoy playing around in Photoshop and Illustrator, I can create my own interactive watch faces with no programming skill required. Watchmaker and other apps allow you to create each element from the background to the hands or dials or readouts or buttons and tie them to variables like time, date, battery, location, or even the orientation of the watch in space.
It's totally a geeky bit of tinkering that not everyone would enjoy but again, there are thousands of great ones out there made and shared by people who are into that sort of thing. Granted there are plenty of shitty "brand" watch knockoff faces and ugly amateurish stuff but that's the nature of user-generated designs.
So yeah, for $150-250, if you're a gadget fan and have the dough to spend on something that's mostly just pretty neat but not necessary, I think these sorts of watches are great. If the idea of putting it on a cradle on the nightstand every night turns you off or you would never spend that much on any watch, maybe it's not a great idea.
I doubt that I would spend the $400-500+ I've seen other smart watches going for because there's only so much I'd pay for a smartphone extender with custom display but in the $150-250 range it's pretty sweet.