Just saw this and have not seen it posted. Mostly positive including heart rate accuracy. Screen is hard to read in the sun. Apple apps are a bit basic.
http://recode.net/2015/04/20/health-and-fitness-on-apple-watch-a-solid-start-with-limitations/
http://recode.net/2015/04/20/health-and-fitness-on-apple-watch-a-solid-start-with-limitations/