- Cookies aren't remembered properly.
- The font cache corrupts and requires restart of the browser at regular interval (unless you like Chinese Unicode squiggles taking the place of your normal page text).
The original coding team were ditched, the replacements were all new - the forums/blogs describing this were purged but you can still find them if you try really hard.
People who start on new versions? If there are less of those than your ENTIRE existing customer base, you're losing out. See replies to this post - a lot of old-time supporters, people who were buyers of the software over a decade ago and still using it, have left it behind.
Bug reports used to be answered. Your snarky answer is precisely the problem - nobody cares about replying to them now. And most of them are literally WILLNOTFIX.
They removed the entire mail and chat clients, the integrated Bittorrent download, the bookmarks, the entire UI customisability (the strongest point of Opera), the kiosk modes, all the stuff that made them unique. Go download a 12.16 and look how many features there are that just aren't there. Nobody uses them? The bug reports, the cries for their return, and the fleeing users suggest otherwise. Don't say they didn't remove features.
Nobody knows that the Desktop version grew. The only numbers you have are from Opera themselves. It was already a niche player.
The dev team CHANGED. It was announced several times on the forums. The old ones were shown the door, the new ones only broke the old codebase and couldn't advance it. It was part of the reason they "started again" - they didn't know how to do anything else (and Linux, etc. clients were left in the wake of the change).
Breaking it? See bugs at top of page - not present in 12.13 (before the dev change), present after and getting worse until 12.x branch was abandoned.
And I used Opera since before 3.6. The number of bugs that weren't replied to, fixed in the next minor and never affected much (except the occasional rendering bug) were few and far between... or I wouldn't have paid for it, wouldn't have used it, wouldn't have fought for it, wouldn't still be mourning the loss of it.
Opera dev team were shown the door, new dev team can't get close to replicating their functionality even after - what - a year or so with NO HTML engine to worry about (Chrome handles all that now)?
If you don't know this stuff, you probably weren't using old Opera or weren't on the forums at the time all this was announced (before the new versions even existed).