When it works, it's not ugly but, vaguely inhuman and austere. A kind of modern Gothic, like a medieval cathedral, overwhelming with dread and awe. Perhaps unsurprisingly it's quite a popular style for modern cathedrals, as well as courthouses, etc.

My hometown, Toronto, is rather infamous for its fondness of brutalism: https://www.instagram.com/torontobrutalist/ I personally used to always hate it but some of it has grown on me.