It's worked pretty well for me. Nice little feature. Can be useful in a lot of situations, not just for "group selfies". For instance, I used to use a little Bluetooth button thingy for snapping the shutter when I'm doing various shots with my iPhone 6+ on a tripod.
Now I can just can just use the Apple Watch for the same purpose, and with the extra benefit of being able to position the iPhone on a GorillaPod in odd spots/angles that would otherwise prevent being able to see the shot your wanting to frame.
The only downside is that it's currently only for still shots, not for shooting video. (I'm sure that will get added someday.)
I think apple purposely didnt make the watch thinner or included the camera because they know people are going to buy their watch, like samsung has a camera but they also have been working on it for years, why couldn't apple copy them?