It's utterly fantastic. What is surprising is how much all the apps have changed - all the functionality was seemingly ripped apart and put back together.
It's definitely rough. This is a beta, not a Google "let's call it beta even though it's actually finished". A real beta. With plenty of bugs; occasional crashes. Lots of graphics glitches esp. when using 3rd party apps. Seems to use tons of battery.
If you don't understand what a beta is, better don't install this. Beta means buggy.
But as far as the UI is concerned, it's fantastic. It's beyond that - it feels as if a great weight has been lifted from iOS and I can feel the blood, sweat, and tears, as well as enthusiasm and sheer euphoria, of the people putting this together in an insane timeframe. 7 months!
Sure there's inconsistencies in the design - those will get fixed over time, probably before the GM; there's so many glitches - I expect some will remain past GM. There's some weirdness that'll only get fixed next year.
But all in all, this is one fantastic update. This is Apple at its best. If you can't see that, I feel sorry for you, but I also feel confident that you will see it in hindsight, next year, when everyone will talk about how Apple re-invented itself yet again with iOS7.
Samsung meanwhile is already hard at work copying all those features, expect them to pop up in Android within the next 6 months. Parallax background will be first.