I'm still on 12.15 64-bit. It still has the vast majority of the latest HTML5 and CSS features and I haven't found many sites that I can't use with it yet. The sites that do stupid checks to stop me from using it are easily bypassed using the built in scripting support (similar to the greasemonkey plugin for other browsers).
The only feature it is really lacking is GPU acceleration.
They should have waited until they implemented more features in the Blink version before they made it the new official version and stopped support for the Presto one. The Blink version is extremely lacking in features and the features are being added way too slowly. It doesn't even seem like they are going to add in all the features from the Presto version.
The reason people used Opera is because of all the features it had that other browsers didn't, the Presto version has nothing special and lacks almost every feature that made Opera great. The old Opera was completely customizable in every way without even needing to download plugins.
I wish they would just open source it so people could continue to improve upon it and keep it up to date with the latest HTML5 and CSS specs, but that is exactly the reason they will not open source it. It would be competing with their own new version.
When people watch me browse the web they think I am some sort of wizard because I magically browse the web and insanely fast using mouse gestures, fully customizable main address bar searching, and all sorts of other features people don't even know exist. I guess I'll just have to hope they make the new Opera good or those features become good enough in Firefox or Chrome.