I wonder how many people need to post about this issue before something happens? I've posted about it at the Opera One release thread and there are countless other posts about the same thing.
This new look is breaking things.
UI is now only new and most definitely not improved.

All right I decided to grab my secondary laptop with smaller screen and take screenshots of both versions to prove that the new version takes up more space and is unpleasant to use. Wall of text at the end of this post.

The new version takes more space and feels "crowded" even when it's a fresh-ish install:

The difference doesn't look that big of a deal when comparing those static screenshots but in actual use it is a real difference. This must change.

I'm currently reverting to old version just so I can browse the internet which is not something a user should have to do to get a good browsing experience. If this doesn't get fixed I must go for another browser even though resaving all my bookmarks, saved passwords and extensions and stuff must be re-entered. It takes time and I would rather use that time to do other stuff.

Also having those sidebar icons in three different places? Fire the guy who thought it would make a good user experience. Seriously.

My eyes are just fine and I find those thumbnails still too small. I can't believe how this big feature was ruined with a single update - or how there is still no way to change the size of them.

My eyes are just fine and I find those thumbnails still too small. I can't believe how this big feature was ruined with a single update - or how there is still no way to change the size of them.

I wonder how many people need to post about this issue before something happens? I've posted about it at the Opera One release thread and there are countless other posts about the same thing.
This new look is breaking things.
UI is now only new and most definitely not improved.

All right I decided to grab my secondary laptop with smaller screen and take screenshots of both versions to prove that the new version takes up more space and is unpleasant to use. Wall of text at the end of this post.

The new version takes more space and feels "crowded" even when it's a fresh-ish install:

The difference doesn't look that big of a deal when comparing those static screenshots but in actual use it is a real difference. This must change.

I'm currently reverting to old version just so I can browse the internet which is not something a user should have to do to get a good browsing experience. If this doesn't get fixed I must go for another browser even though resaving all my bookmarks, saved passwords and extensions and stuff must be re-entered. It takes time and I would rather use that time to do other stuff.

Also having those sidebar icons in three different places? Fire the guy who thought it would make a good user experience. Seriously.

@nadie-nada-nunca I must hop in here. Because I must ask; do you like it more than previous UI?

This ridiculously big spacing everywhere around icons and stuff is breaking the browsing experience on smaller screens/resolutions. It eats up precious screen space so there is even less vertical space for actual page content. It's not that big deal on QHD monitors but on 14" FHD screen with 150% increased scaling, it has a massive impact as every pixel matters.

I love to see tab grouping coming back but I'd prefer to see the whole page name instead of only a colored bar when it's collapsed and inactive. I currently have two tab islands collapsed with very similar colors (red and is maybe orange) and I already forgot what's inside them. So color alone is not that great when I later need to find specific website.

Also as I'm using Windows 10, this new UI looks completely out of place. We deserve more options for the UI: first named "Default" (which is this current version) and second "Give the old back" (as the name implies, the old look).

@rh99 Actually it is very useful feature and one of the biggest ones I used that were present in Presto version of Opera. It allows us to open loads of tabs and then pack them to take less space on the tab bar.
Tab islands is just a fancy name for tab grouping. Having multiple windows open is a no go because it eats up task bar space and is just generally more clunky way to switch between stuff, especially for those who prefer to keep it hidden.