You notice ugliness everytime you use it. The beauty in UX/UI/Window Manager lies in it just being there, not distracting but complementing one when he/she is working.

That's my definition of beauty. I can go days without noticing it and if I take a step back and take in the whole experience, I find the beauty.

Ubuntu does it for me. Especially because I can take time to make it beautiful for me and I can have a free hand while doing it.