Well the first thing is that it is a beta and I don't expect public release quality. I don't like the weather app. It cuts off the edges of the font. Animations are choppy and there is a delay in response time when I press on an app to launch. When I use spotlight to search and launch an app, it keeps the results in search instead of a clean slate when I use it again. Apple Music doesn't work right and says I am offline when I try to look at For You. Like I said, this is a beta and I do expect issues and bugs (like the inability to use the volume button to take pics).
Also, since I have good 8.4 backups, I don't want to start getting into using 9 for extended amount of time and then an issue crops up and I have to go to an older backup and lose some settings or texts or call history that may have changed. For instance, right now I am restoring to 8.4. My backup was at 11 last night and being this early in the morning, I am not losing much stuff...if any. Had I been using beta 1 and then something in beta 3 broke a necessary function, I would have to restore from the last release of 8.x and would lose about a month of changes.
I can usually find out in one hour if a beta will work for me.