Aside from the bugs, and the fact that way too many apps aren't working, the only thing I really dislike is the lack of color in the finder icons. Luckily, this can be changed.
I do miss the pill button to collapse toolbars.
Oh, and the Launchpad is useless, but I don't care that it's there because it's totally optional.
The background for dashboard is awful, but if you uncheck the option that makes dashboard act as a space, it's gone.
Oh, and the "book" UI for Address Book is really silly.
The mission control UI is nice and I do prefer it to the old way, but it needs some work. If you have more than 9 spaces (I don't) it becomes a mess. Also, you can't conveniently move between 4 spaces via the arrow keys because spaces are only orientated horizontally.
Now my likes: the UI tweaks, Versions, and app persistence/restore are all awesome (My 3 favorite features). The animation for going back in Safari is quite clever and actually useful. The Mail UI is much much better.
Oh, and almost everything animates now. One could consider this a good or bad thing, depending on your taste.