I ran Slackware for ~6 years, my first serious distro. It's kind of the perfect learning distro for Linux - a super stable base, but if you want more you need to learn how to do it yourself. You didn't need to compile your own kernel or set up tons of configuration just to boot, but if you wanted certain graphics drivers or other software, you quickly learned how to write shell scripts and manage builds and dependencies. I remember spending quite a few hours learning how to build my own media stack with mpv and all dependencies (Slackware only shipped with MPlayer in those days, and with no system ffmpeg). I found it to be a much better experience for that than other distros like Arch or Void, those are just too much at the beginning. Because of Slackware, for a good while my most comfortable programming language was bash!

I stopped using it when I had less time for tweaking my computer in my life (I moved to Debian), but it was a very formative experience. Good defaults, but with all the power to change whatever you want and the simplicity to make it manageable.

Happy birthday Slackware!