I love the uses of the sidebar and other features after coming from Chrome, however it feels restricted and leaves a higher level of customization to be desired.
Two huge features would push Opera past Chrome and Firefox; the first would be the ability to rearrange and regroup the GX sidebar, including the ability to close groups of tools and change the icons for each tool, as well as moving the bar to either side (and either side of the scroll bar when on the left) or the top/bottom of the window. I find myself searching for 10+ seconds with the simple icons because they all have similar colors of just the outline, and if we're not able do custom icons we should be able to change each icons color for easier recognition at the very least.
Secondly I want to be able to put tabs into groups similar to Chrome, I feel like the workspaces are limited and allow for much less usability. With Chromes tab groups you are able to move any group to any window with ease, or have two groups set to each half of the screen. With workspaces I'm not able to move tabs so effortlessly and as far as I know you're unable to open a workspace in a separate window. Either improving the Workspace function or adding tab grouping would help to streamline organization of tabs.
The last small customization feature I would like is being able to move the Menu dropdown from the top left, personally I would like it to trade places with the easy setup dropdown. In reality the next generation browser would allow you to move everything from the search bar to the scroll bar, this would make the browser nearly unlimited personal customization for the oddballs who would prefer the tabs at the bottom of the window or their bookmarks bar above the search bar.