I am a KDE user since my first steps towards Linux. Currently, my OS is KDE Neon and I am very pleased with it! Apart from very few minor occasional bumps, everything works amazingly well and I get the most updated pieces of software possible :)
My music player has been Amarok for a long (long!) time. It was always successful in allowing to navigating my music by folder instead of trying to categorize and organize it for me. However, since KDE 5, Amarok is stuck in time. Slow and without any new features. After a couple of attempts, I found Clementine. My first impression was: it does the job, even though it does not look great.
Clementine has all the basic features that you expect from a music player, including my must-have folder navigation. It also integrates very well with Plasma. But the tipping point was the "Complete tags automatically" feature: it connects to online databases and suggest the most likely tags for your mp3 files. It works perfectly and it is very handy! No need of using external software and I can progressively improve the organization of my collection.
After finding that feature, I decided to make it look a bit better and faster and you can see how it looks for me now in the image below.
And here is how you can get the same look:
Some day I will tweak the icons to make them even plainer, but even before that Clementine is my favorite music player on linux!