Opera had had its highs and lows, the Internet experience nowadays is great, much better than the last days of Presto engine. Internet navigation today is quite the same across browsers, it is like using Windows or Mac, both can do all you want, you just linger on the platform you are used to.
The moment you change to another platform is when the devs have changed the things that made you use it in the first place. Years ago, I used Opera because it was the fastest, then I used it because of the speed dial and now, I keep seeing the thing I most love in Opera being messed each version.
Today, the only customization available is to change the background. Prior to chromium, I had widgets there, gmail for speed dial, exchange rates... I confess I hated the dial's size, it was too big. Then, we moved to a non-widget UI, then a UI with smaller dials (that size was great btw) and now back to big dials and no widgets.
As a developer, I know that a great UI is one that doesn't requires (too much) reading. Now, just a few websites have Icons recognized, many became just a domain name and worse, some became a white box (i.e web.whatsapp).
In my point of view, the speed dial is much like Windows new start screen, it is a place that you don't read, you just know where to click to get where you want.
Simple solutions would be to allow us to resize the blocks (they can all be the same size, no problem with that). Allow us to set custom names and thumbnails to the dials. Some more advanced modificastions would be to allow us to make groups or move then around creating custom non-grid layouts.
Another issue, IMO, is the new bookmark. I was fascinated with stash. It was so simple, but so powerfull. By using screenshots of the pages, I were able to find everything stashed in a matter of seconds. I even had pointers like "that link is after that cute cat photo".
A good point against the Stash layout was that it demanded a good amount of scrolling. This could be easily handled if we could have multiple stashes (side by side). I could use one for links, another for gifs and photos and so on.
In sum, stop taking customization away from us and throwing away excellent ideas. The tab stacking thing is also something that I miss very much.
Thank you for your time reading this. I can give more feedback on those topics if needed.