I had the GM on my 5S from Wednesday until about an hour ago. The battery life was abysmal. (about 9-10 hours standby and 3 hours of use dropped me to ~20% every day). Additionally, there was intermittent but quite frequent stutter and dropped frames during animations, usually on the app switcher and when opening the control center or notifications. It just felt sluggish and clunky compared to 8.4.1. This was all from a clean restore and set up as new device.
I just dropped back to 8.4.1. I really hope this GM is not the same version as the public release coming Wednesday. I will probably be waiting until 9.0.x or beyond if the 5S battery life issue isn't resolved. What sucks the most is I already put watchOS 2 on my watch, so I can't use that again until I upgrade to a usable build of iOS 9...