I don't know about all of you, I don't like these new flat icons that everyone is using. What ever happened to the old icons, like on iPhone and Samsung they used to have them years ago. Those were good times. Now it is always these stupid boring cartoonish designed icons. Side note: Somebody please update this icon pack. I am trying to use it on xfce on arch but some of the icons aren't working properly because it hasn't been updated in a while. I'll donate to you right away if you do it. Link to the repo: https://github.com/madmaxms/iconpack-obsidian
Actually no, I hated the Vista era UI design. Linux themes were positively garish, add MacOS looked like a candy store. CDE greatly impressed me back then. It looked like it was made by adults for adults. Highly legible, and the pastel colors are being emulated by Solarized.
I'm sure that those UIs were a product of the times. The 90's and noughties were loud and colorful and exciting and everything looked like a comic. Now that we live in more depressing times, we can look to the science of perceptual psychology.
You see, we have an attention budget, we need to process what we see. Visually complex UIs need to be parsed, and that takes mental effort, and that robs us of mental energy to focus on our work. It's not a crippling effect, but it's there.
Look at street signs and corporate logos, they easily lodge in our mind. Effective advertising has a clear and simple visual language, and this is what UIs should strive for.
Interfaces can be needlessly complex regardless of being flat or skeuomorphic.
But flat interfaces still require mental effort to parse. Especially when the interface is complex and/or crowded and you're trying to pick out active UI elements amongst decorations like group boxes/panels.
Essentially, flat interfaces are currently popular because of touchscreen devices. Touchscreen devices have limited space and thus need simplistic UI elements that can be prodded by a fat finger on a small screen.
But I don't need a flat touchscreen-friendly interface on my non-touch dual 24" monitors with acres of screen real estate. I need an interface that nicely separates usable UI elements from the rest of the application window. That means 3D hints on a 2D screen, which allows my monkey-brain with five million years of evolved 3D vision the opportunity to run my "click the button" mental command as a background process.
One of the reasons i like interfaces with clear lines. But that doesn't fit icons, all-same-isch looking rectangles are not easier to parse than "objects". The mind is optimized for 3D, not for abstract icons.