The sad thing is that if Opera 12 is/was your favorite browser (as is mine), you will very likely hate Opera 15+, because it is the very opposite of everything that made O12 great. O12 was the most customizable browser and O15+ is just a mediocre Chrome clone.
Opera is actually doing their Linux users a service (albeit not on purpose) by not letting them see the travesty of a browser that now bears their name. I wish there was no Opera 15+ for Windows, at least then I would keep the hope for more good versions, instead of knowing that the best browser has died.
By the way, there is a project to create a free browser inspired in O12- - http://www.otter-browser.org/