I use Opera everyday at work.
I've become quite used to its UI, I hope they don't change that.
From the old Presto based Opera, one of the most frustruating aspects was searching for text, especially in very large auto-generated webpages (ie webpages which contain output of test runs, etc...) Opera's search there was painfully slow compared to Chrome/Firefox/etc...
There were also compatibility issues with a couple of sites, but this was just minor stuff I'd ignore. The UI with Bookmarks sidepanel/RSS/Integrated Downloads manager (with torrents)/SpeedDial/ was what sold Opera over the rest. Another feature was the password manager, I have to sign on to dozens of internal sites, reauthenticating at every access, so if you open up a dozen links to the same portal, in Firefox each prompted for a password, but in Opera, enter a password for one of them and they all just unlocked, it was lovely. This isn't the kind of stuff to put on banners, but man it made me happy and productive. The little things.
I hope they haven't removed any of what I like, it'll be quite sad.