I was disappointed too, when I learned that the AW would not have its own internal GPS. But then, I bought one anyway.
I have only run a few times, but so far the HR sensor has been perfect-- it exactly matches my Garmin 910XT.
However, I do not think that the AW will ever be a suitable replacement for a dedicated running watch. The Workout app has several shortcomings, including the fact it does not map your run, it cannot show cadence, it does not have elevation, and it cannot show mile or KM splits. So, if you are a runner that is looking for a watch as a tool for recording and helping analyze performance, the AW will likely never be there. But, it is a great running companion to an iPhone, for those days when you do run with a phone.
My recommendation for runners is to get both an AW and a Garmin/TomTom/etc. running watch if you can afford it. If you cannot afford both, but want some smart watch features, get a Garmin Fenix 3.