From the recent changes it's obvious what they want to achieve. They want to abandon the traditional Q&A model in favour of a Reddit style forum. This is in line with the recent addition of opinion based questions, as well as the upcoming removal of close votes and review queues.
The UI itself is awful, the dark mode is way too dark, and the answers look too similar to the comments around them (just like on Reddit), so it's difficult to scan the page for answers. Why they decided that all comments must be expanded by default is beyond me, it takes up so much vertical space for something so irrelevant. The meta info on answers (score, accepted, poster, etc) is not prominent enough. The new design uses too little colour.
This question shows the problem quite well: https://beta.stackoverflow.com/questions/11227809/why-is-processing-a-sorted-array-faster-than-processing-an-unsorted-array
Did you notice Daniel Fischer's answer?
Tap for spoiler
I don't think the new design is ugly per se, it's just less usable and less visually distinctive...

