So far, I've been finding very little that I've had a problem with while testing aside from the odd bug or two. In fact, I've been finding a great deal that I really, really like. *Very* impressed with the work that's been going in to this expansion.
However, one thing bugs me a great deal; UI color sets are saved between all of your characters. Sure, I could work around this by going through the options, but it can sometimes be a hassle to go through the 1-2+ layers of options to change the settings for each character, especially if I'm switching back and forth between characters fairly often.
Wouldn't it be better to set it up so that the system can remember UI color scheme settings on a per-character basis, as opposed to per-account? It can be quite jarring, to say the least, to switch to another character of a different faction, yet have the color scheme of the previous character remain.
P.S. There is also a bug related to this issue, in that ability icons will remain with the colors of the previously selected UI color scheme if another character is switched to and then the color scheme is changed.