This would better be posted on the mailing list, as this server is for code review. However, we completed a large-scale UI refresh in 2.5 already. Not sure what version you're running.
updated ui for Review Board
Review Request #8125 — Created April 20, 2016 and discarded
I am posting this here to see if there is any interest from the community to update the UI. I would be willing to do the work, if it would be welcomed. We use Review Board where I work, and so far it has been a good tool for our workflow. The only complaint I have heard is the UI seems dated and could be improved. Does anyone have any thoughts / opinions one way or the other on this?