It doesn't really sucks. Instead, I'm happy I have no longer to put up with the growing number of Windows annoyances. The balance is definitely positive.
That said, there are a number of issues that I've found. Some of them are solvable via configuration, some of them are not. I'll omit a couple of bugs I submitted to KDE that they say are corrected in the new version. Unfortunately, it seems I'll have to wait a long time until that version is published and then reaches Debian stable.
- KDE look and feel customization is badly scattered in multiple menus. Some options are not accessible and need to be changed in scripts written in a KDE-specific language. There are a couple of very bad UX in the last category.
- Firefox, Thunderbird and other applications use completely different file dialogs with different conventions that I haven't found how to configure. Firefox is more difficult to configure than it seems. I started caring because it had tiny scrool bars. For some appearance configurations I had to look at Firefox source code.
- My Behringer external sound interface doesn't work with the default software. It works with Jack, but I've been unable to configure JackD to start automatically, so I need to start it manually every time I reboot. Mitigated because I always hibernate.
- Drag & drop works in a very weird fashion. When I drop something, a popup menu appears asking me if I want to copy, move or link the dragged item. There's no way to configure KDE to just move. I need to press shift before I start dragging and that conflicts with multiple selection... no way to move multiple files without the shitty menu.
What I found sad was the response to users' request in forums. Some users volunteered solutions and they were told that they won't be included because the fixes needed to be included in some config dialog, documented, translated to all languages... and noone will have time to do all that.
One thing that I had not thought about was the increasing complexity of code bases. I looked what I needed to compile a browser, not sure if it was Firefox or Chromium, 500 GB required. Firefox also needs Rust now.
I'm worried that the OSS projects have no enough volunteers and the barrier-to-entry is high enough to discourage more people helping.