I just want to thank this thread for telling me about Vivaldi.
I've been using Opera since back when you had to pay for it (which I gladly did).
One of the reasons I loved it was the fact that everything was customizable, which is something that has being going away ever since the Presto engine went bye-bye.
Another reason was the small, innovative features that set it apart from the mainstream browsers, like mouse gestures, links and info panel, Dragonfly, recently closed tabs, completely custom search engines, etc.
Many of those things have already disappeared into the sunset, or replaced by more generic functionality copied from other browsers, and like many people in this thread, the recently closed tabs functionality just being removed (twice) was the straw that broke the camel's back for me. It's a feature I use instinctively, and not having it in that spot hopelessly slows down my browsing.
Within 10 minutes of installing Vivaldi, I was back at the browser Opera used to be.
Sad to say goodbye, but as others have pointed out, Opera has been steadily becoming more 'our-way-or-no-way'. And if I wanted that, I'd be using Firefox or Chrome. I understand it is a free product, but I was happily paying for it before it became free, and would gladly still do so if it meant getting the old, innovative Opera back, instead of this paid-for-by-Google Chrome cosplayer.