UI still needs important work
Love the idea, all strength to it. Sadly, there seems to have been too little progress on the UI front.
There is still no single tab close button - all versions of real Opera up to and including 12.16 have this; so does Sea Monkey, so does Pale Moon, so does Firefox (albeit only via extension since the Firefox UI wreckers went mad on Australis). For many power users this is a use/avoid level feature. (Count me amongst them.)
There is still no obvious way to get a clean page without that annoying and useless panel bar down the left-hand side of the screen - you can move it but I can't find a way to get rid of it.CORRECTION: there is a way now, but it's not obvious - you have to find a little icon in the bottom left corner. Once you do though, it apparently works fine. All that's needed to complete this improvement now is put that setting where it belongs: in settings -> panel.
I won't list more minor things as the improvements are coming along nicely and I'm confident they will be sorted soon enough.
Without a single tab close button (i.e., an option to have the control to close the current tab always in the same place where it can be used automatically and without conscious thought - nothing worse in a UI than having to search for basic controls that move around) I can't view Vivaldi as a possibility for prime time use yet, but this latest version seems good enough now to replace Chrome as the 5th-choice browser on my machine. (And yes, I do use all five.)
Very keen to see Vivaldi progress: it's got nearly all the parts in place now.
PS: get it right - that means a modern browser with a UI as good as or better than Opera 12.x - and I'd be happy to pay cash money for it. I know they are looking at other ways of funding it, nevertheless, for many of us our browser is the single most-often-used program on our computers. If it cost $100 to have a better browser, I'd pay without an instant's hesitation.