It's not stand-alone outside of those times you're using it for fitness--meaning, without an iPhone, you can't use it at all. First thing you need to do to even "wake up" the watch is pair it with an iPhone. You need the phone to upgrade software onto the watch and put apps on the watch, or to download a playlist of music onto the watch.
So, while the AW2 will be able to chart your calories and such on a run or hike walk or swim, and, thanks to GPS, know where you are, and even give you music to listen to on the run, walk or hike...it's not iPhone free by any stretch. Remember, it's also about being able to get messages on your wrist, phone calls if you want, mail, reminders, etc. All that requires the iPhone.
So. It's kinda chained to the iPhone for now and probably will be for a few more years at least.
Cheers, thanks a lot for the details!