My only criticism of the dark theme so far is that links within a post are no longer obvious because they are the same color as the rest of the text. The dark theme would currently require a user to mouse over all the words in the post to determine if there was a link present.
I have linked the RadioReference website as an example.
Not just links are dark with the dark theme, some posts contents is also dark. I must drag across it like I'm highlighting to copy it in order to read it. I barely noticed then when a post in a thread seemed empty of any content. I looked a little closer and sure enough, there was reversed text barely visible in the post!
So as much as the default theme blinds me, I've gone back to it due to the above reasons.
I can only hope they will allow some of the many other available theme's available for Xenforo.