Drag highlighted text to the new tab "+"
In experimenting switching from Chrome to Opera, this is one feature I didn't realise how much I use until I found Opera didn't have it.
In Chrome, it is possible to highlight text on a webpage, and click-and-drag it up to the new tab "+" at the top of the screen (or to the URL/search box in your current tab). Upon releasing the mouse, Chrome will open a new tab and search/navigate to the thing you dropped there (or search/navigate to it in your current tab, automatically redirecting you).
The closest Opera manages is allowing you to drag-and-drop text into the URL/searchbar of your current tab, but only pastes the text inside the current URL. For example if I dragged the term "Sennheiser" into the tab from Amazon, I'd get something like "www.amazon.co.uk/xxxxxxxSennheiserxxx" and then does nothing, whereas Chrome would delete the Amazon URL and search for Sennheiser.
I realise Opera allows you to right-click and search that way (as does Chrome), but dragging feels smoother and more intuitive: It is rare to have to use the right mouse button when browsing the internet, so being forced to do so breaks your flow.