For a long time I did all my personal browsing using Opera browser. The Presto engine‘s wacky-ness here&there was tolerable, because it just felt like a power-user’s browser, will a full arsenal of customizations at your disposal. On May 28 2013, Opera 15 (which ditched Presto in favor of the WebKit-forked Blink engine) has been a pretty large disappointment. Gone are Bookmarks, Opera Link/Turbo, essentially all of the Tab functionality, Mouse-Gestures, Keyboard Shortcuts, Download Manager, and about everything else that made it appealing. As others have already said, it feels like a Chrome skin.
I suppose I understand the motivations behind switching to Blink, but there does seem to be the caveat of creating a monoculture with regard to the rendering-engines. Hopefully they decide to make Presto open-source, so that others may continue developing it.