I just got it this morning (Sprint, east coast USA) and love it so far.
Among a noticeable speed upgrade, the keyboard now slides on and off the screen and the battery meter is white.
The "Clear" button in the notification panel appears to be bigger, which is nice for those of us with normal sized fingers.
The only bug I've noticed is the black default menus now "smudge" really bad. But if this is the only bug, I'll take it along with all of the changes.
Got mine this morning on US Cellular. So far everything is working well, including Flappy Bird. It was a simple download and install- no issues. Apart from the all white notification bar, new font, and full album art on the lock screen when you play music, I don't notice many new changes. I use nova launcher and an icon pack, so I haven't noticed any changes there (I heard Touchwiz UI is supposed to be much faster). It feels smooth, and everything has been working normally (including with my Pebble).