I think the new UI is nice, I'll have try it to really see how it fits. I don't see that many features though. Search and continuity. I'm not entirely in the apple ecosystem so the latter doesn't mean too much to me. Search looks ok, I guess.
I like most of it. Especially continuity. They went nuts with the transparency, though. I think it'll look terrible with lots of overlapping windows onscreen. Reminds me of 10.0 in that respect. Hopefully they will dial it down before the release. Luckily the icons did not inherit iOS 7's ugliness, except for maybe the folders.
Dark Mode could be nice...does anyone know if it affects windows in general and not just the menu? I wonder if it's the new interface's "Graphite," and makes the stoplight buttons grey...
None of the features are useful or interesting to me. I don't care about UI in general, so I'm indifferent to that change. Several features make me specifically not want it, such as searching the internet with Spotlight due to privacy reasons.