Thank you so much for this thread. Opera became almost unusable for me and i could not figure out what caused the problem. It began with extensions (smartRSS, Pushbullet, some Bookmark extensions) which were not rendered anymore (or just contained strange patterns of the topright area in weird colours), then regular websites were empty as described here and only restarting the browser multiple times helped in a few cases. Now, disabling hardware acceleration did the trick for me, and all the mentioned problems are gone.
(On Fedora 23, using the russianfedora-RPMs)