A flop? Wow. What device are you using? An iPhone 4 or something!!
iOS 9 on my 6 is pretty darn good for a BETA. Just though I'd capitalise the important word there, a BETA.
I installed beta 5 on my iPhone 6. It was buggy, sluggish and not at all fluid. My device heated up like an oven and battery drained considerably. Gave it a few days and just simply couldn't take it anymore and downgrade back to 8.4.1. Perhaps some people have better experience with beta 5, but I expect the experience to be the same for 100% of idevices before it gets launched to the public.
Yes this is a beta but the whole point of a beta is for a) developers to get their apps to function on iOS 9 and b) iron out all bugs and ensure the public release is stable, fast and fluid.
Failure to do b) is a failure for the public release IMHO.