They should have spent more time on this one...
Having put up with the 10.50-release of Opera for about 2 days now, I gave up and rolled back to 10.10.
I don't mind reconfiguring some of the settings when upgrading to an newer release, as long as I am satisfied with the end result.
For some reason, the new Opera-Symbol containing all the options previously found in the menu bar, didn't show up for me in any of the skins (including the ones that shipped with 10.50). After having found out about the existence of the O-Symbol in itself online and then having added it manually over the appearance-dialog, I was able to get the usual menu-bar back.
Other problems couldn't be solved as easily. For example, the address bar is a total mess compared to the one of its predecessor.
No matter what you type, the first entry in the dropdown-list seems to be "Search the web for 'typed stuff'", instead of the "most logical auto-completed address found in the browsing history", as it used to be. If I want to search the web for something, I'll use the search-box or one of my customized search-keywords, thank you!
This behaviour can't be altered or customized at all, like to mimic the address bar of previous opera versions.
The new inline-search, which is glued to the top toolbar instead of floating freely like before, doesn't bother me that much. The dimming of the screen is actually quite nice and usability-wise the searching feels not so different than in 10.10.
The Search-box in the toolbar on the other hand has taken a turn for the worse, by expanding the complete list of custom-searches plus a few of recently entered search-terms every time you start typing in it. Given a sufficiently large enough list of searches (like mine, for example), this dropdown-list clutters the screen completely unnecessarily and just distracts from typing.
The deal breaker, however, was the inability of Opera 10.50, to map the Wand-function to Mouse-Buttons. Many users (including me) were used to log in to known websites or fill in saved forms by pressing the forward-mouse-button. (Like the one on the side of a Logitech G5)
In 10.50, this particular function seems to be ignored, when mapped to mouse buttons. Binding other actions to mouse-buttons works perfectly fine and configuring different keyboard-shortcuts for the wand does as well!
The condescending attitude, with which some of the senior forum-members at the opera-support-forum treat the reporting of bugs is quite disgraceful and I wouldn't be surprised, if this behaviour costs them a few of the new opera-users who just started with 10.50.
I can only advise everyone, who is thinking of an update to the newest version, to consider the matter very carefully. A glance at the support-forums should reveal most of the bugs, one might encounter and it's up to personal preference and requirements, if one of them is severe enough to justify keeping the current version.