While it's not as terrible as Lion was, I'm not entirely happy with it either: the interface seems laggy and slow, the whole thing seems slower than Mavericks. Switching spaces isn't very responsive and animations are choppy everywhere. Running on a Late 2013 rMBP with 16 GB of RAM, everything should really run as fast as hell.
I do like the interface though, however, the font is a bit strange and looks a little bit cluttered instead of being nicely spaced out.
Oh, one thing I hate: the "waiting" progress bar (which used to look like a stripy blue/white candy bar flowing backwards) now looks almost exactly like a normal blue progress bar at 100%. So before every file transfer, for a few seconds, it looks like the file transfer is complete even though it's just waiting to start. This is very lame.