I'm an Opera user since I switched from Netscape Navigator (remember this one?). Since v15, I used 12.16 exclusively, with sometimes Chrome as backup. Today I decided to try out the new version, and hooray, extensions are back.
But many great things are missing, or impossible to find:
-the new config is a joke (or the real config menu is really, really well hidden), for example no option to disable speeddial?!?
-after looking through this thread, I didn't even bother to import my several hundred bookmarks.
-no tab groups? Easily one of the Opera features I used the most, and SO practical! Gone, but why..?? Gamebreaker right there.

-it also had some problems with the "back" button, used in my eMail account, if reading a Mail, and clicking "back", it brought me not into the inbox (what I want and the old browser effortlessly did), but straight onto the homepage

I have now downloaded 12.14 again and will use it together with Chrome (which btw removed the speed dial as default setting) for the few sites that give the old Opera problems.
Opera20 is a step into the right direction, but it definitely lacks many good features.