The last true version of Opera was 12.18, which is slowly bit-rotting to death, e.g. a number of modern https ciphers simply don't work.
Opera ASA then jumped to v15, which was a chrome fork with some branding, half-heartedly added a handful of features, and tried to pretend Opera 12 never happened.
Then the browser part of the business was sold to a chinese malware company.
And the tragedy is that Opera was the most innovative and light browser out of all of them. I used to run Opera on my old machine with 16 MB of RAM because it was literally the only browser that was usable.
Mouse gestures, tabs, integrated mail/rss/newsgroups client, and even a fricking web app platform for personal use made it the best browser then, and even now. It was always standards-compliant, but got a bad rap because of lazy designers who just tested in FF and IE and called it a day.
Opera Unite, in particular, the web app platform, was fantastic. They gave you a dynamic hostname with Opera and allowed you to run apps like photo albums and blogs straight from your browser (which had an embedded webserver if you enabled the feature), so people could publish their content completely decentralized, right from their computer and browser.
Opera ASA then jumped to v15, which was a chrome fork with some branding, half-heartedly added a handful of features, and tried to pretend Opera 12 never happened.
Then the browser part of the business was sold to a chinese malware company.