I'm so impressed with the UI and execution. Very well done. No complaints, except that it's perhaps the move timer is a little fast.
I first learned about Ultimate Tic Tac Toe here[1]. Might be worth a link to that post -- it's a great explanation with surprisingly satisfying illustrations.
[1]: http://mathwithbaddrawings.com/2013/06/16/ultimate-tic-tac-t...