So one change I've found that seems to have flown under the radar of most people is how custom portraits are handled. It used to be that the scroller showed only the default portraits while the custom button showed two lists so we could pick a separate small portrait for the party list, and large portrait for the character sheet.
In the 2.0 beta, all the portraits are in the scroller, making it a pain in the ass to scroll past the great volumes of custom portraits I have installed (and really, who doesn't? I don't want my character stealing the appearance of someone else in the game), and we now can't pick a separate small portrait, which is a pain in the ass since a lot of portraits (IWD's a re a great example) are designed to be full body shots on the character sheet, with a close up on the party list. Now we have to chose between the full body shot in both places, where in the party list you're just going to look like a stick honestly, or the close up, which is going to be blurry and/or pixelated as all hell on the character sheet. There's no right answer.
Can we please have the handling of custom portraits reverted. This change is terrible. I can find silver lining and reasoning behind every single other UI change in 2.0, but this is bordering on punishing players for using custom portraits and I can't understand why you want to do that.