The new browser is not entirely bad, there are good things about it. I imagine it achieving some success in capturing a new audience. I wouldn't even say the new concept is bad despite the lack of refinement at the current state (inconsistent and sometimes unnecessary borders, too much wasted space, questionable accent color, etc.). But you know, the problems themselves are not even the problem here, it's how the new design was forced as an update. The developers must understand there are tons of browsers out there and previous Opera users chose it for the particular experience it provided, so to force a entirely new experience like this assuming they'll want it is unreasonable. We're not a cult, we will not just go along with anything. If it's a entirely new experience and the previous one is gone, users will obviously reevaluate their choice and maybe will stick with the new browser. And good luck with that.
It's ok to change, to try to evolve, but you should be more careful than that.