The "real" Opera is still my favourite browser (since 1999) and my only mail-client but due to its age every day there are more pages that can't be displayed properly.
I tried the current Chromium-based Opera two or three years ago and didn't like it. As it was clear that it wouldn't get a mail-client I was also put off.
For pages that can't be displayed in Opera 12 I use Vivaldi (Chromium-based) which is making progress but still lacks several features Opera has, not only the mail-client which is said to be added until the end of the year. Then Vivaldi would be a replacement for Opera.
Another alternative I sometimes use is Otter (in Sparky's repo or more recent versions at https://launchpad.net/~otter-browser/+archive/ubuntu/weekly/+packages
). It started nicely but development is slow, so I have doubts whether it will ever get the planned mail-client.