Updated from iOS 8.4 yesterday, having not used any of the previous betas. So far, everything seems to work fairly well. Some apps are a bit crashy, but nothing yet has outright refused to run. Battery life feels unchanged.
My biggest overall complaint is that the OS is just not nearly as fluid. It's not consistent or debilitating, but it's annoying. There's a delay when opening apps, delays when opening the app switcher, sometimes controls, gestures, or scroll areas don't respond immediately, sometimes things freeze for a couple seconds. It kind of reminds me how the GM release of 8 was. Again, nothing unusable, but I sure hope it's better for the GM build.