For the last two minor Opera 64-bit releases (incl. the last one 44.0.2510.1218) I have issues with their installation. Installers freeze the moment it used to bring up the "default programs" window in the past. Now it can't bring it and stays open forever.
The only feasible option is to kill the installer process. If I'm trying to close it, then rolling back fails as well and Opera reverts back to the earlier version. However it's not possible to run installer anymore - after accepting installation it immediately encounters an installation error and quits.