For work I use the JetBrains IDE PyCharm and CLion. The UI generally has a high information density and one can display tons of little panels. They now have a new UI which they urged me to try out. But I am not impressed at all, I find it to be a big step backwards.
My PyCharm looks like this for a small project. I have a file browser open in the left top panel, and the structure view on the left bottom panel. As you can see by the little handles on the border, there are many more panels on the bottom and more panels on the right that I can expand. And then there is a menu bar as well as a full toolbar.
I like working with that. But then I tried to enable the new UI in the settings.
It really looks like VS Code afterwards. I mean, that might be cool, but look how little information there is now. In the following screenshot the panels are folded in, I'll show them later. But the toolbar is gone, which I find annoying. And the main menu is collapsed with in the hamburger menu, which means one additional click with the mouse to get it.
The panels can still go to the side, but I cannot have panels in the upper and lower left and right sides. This means that I can only have one thing in the sidebar each, which is already bad. See how much screen is wasted by having the project explorer and the structure view on either side? On top of each other it just makes more sense. On a large screen I can then have a split window open. But here I cannot.
The only other way is to move these to the bottom. But for bullet list like things the bottom doesn't make so much sense. The terminal is fine there, but the structure doesn't make sense there. I need something with a portrait aspect ratio.
So my verdict on the new UI is that it is like so many things these days. They tried to reduce information density in the quest to remove clutter, but in this way they removed important things. Through keyboard shortcuts I might be able to get the functionality back. Or I have to switch the panes all the time. Either way, I think that this is a step back.