One of the most impressive and useful free software projects. My first experience was being totally confused by KDE 1 during my first attempts to use Linux, and I'm writing this from my KDE desktop.
Other than the really bad KDE 4 release, the project has consistently been great for me. I've submitted a few smaller patches over the years and that experience was also low friction for a project of this size. KDE is highly customizable, full of power user features but also really simple with its current defaults (looks pretty much like Windows) and generally robust.
Shoutout to some KDE applications like Okular (great document viewer), Kate (solid tech editor), Krusader (double pane file manager) and KolourPaint (a simple image editor even I can use).
I agree it's really impressive, it brings a lot of things together into a cohesive package and experience. I'm a huge evangelist, I think it's the best desktop experience.
I remember when it first came out. Very impressive at the time. I was never a fan though personally, I always hated the look of KDE. I used it recently on CachyOS for fun and it worked great, just not for me visually. I'm glad it exists, I just wish there was something visually appealing with less settings bloat. It feels like going to a diner with 300 items on the menu and they're all sorta half baked.
I've been using KDE for the last 30 years I guess but somehow never used KolourPaint until to 2 weeks go. That's the first "pain" program that is usable to do simple things. Gimp is waaaaay to complex for simple tasks (especially the selection which I've never understood). Congrats KolourPaint team for KISS.