Flash 11.7.700.169 installer downloads exactly 50% of its assets, Installer starts, then fails. This is on a year-old 27" Core i5 iMac. I've tried removing traces of old versions, .plist files. A newer 17" MacBook Pro Core i7 laptop installed without a hitch. NOTE: the help page which advised launching the installer by drilling down into the application's Contents is useless, as the current installer looks nothing like that.
Workaround: Logged out of admin account, launched the installer from the Guest account, entering admin credentials as often as requested. This was successful, just not optimal. Hopefully the next update won't show the problem behavior!