No problems on my iPhone or iPad.
I have it on an iPad 3rd gen., iPhone 5, iPhone 6, and iPad Air 2. Works fine. No crashes what so ever.
No problem downloading either. At that was on the first day.
iOS 9 Beta program participant - was a fairly smooth beta run. I was rolled to the 9.1 beta just before the general release of iOS 9. So far, pretty functional. No major issues at all.
I seriously suspect at least SOME of the issues are related to folks who fill their devices with garbage, leaving little to no space for the iOS updates to download and install properly. No different than a PC with a nearly-full hard drive, with a user that just doesn’t “get it” why stuff runs slowly - and software updates take forever, and often create issues...
I am not going to discount that some users may have issues through no fault of their own... but I would suggest that is the exception, rather than the rule - But we also know that the loudest voices on such things are those who DO have issues.