Thanks a lot for the detailed comment.
Yeah, the difficulty level selector was a huge mistake, but also an important lesson about how doing something anti-intuitive can ruin the player experience. I agree on everything you said about Pacman: I just run out of time and had to spend the whole last day fixing the AI for html export.
Fun thing about the tetris game is that you can actually help any of both 'teams', in case you decide to don't force your brain and play tetris as you are supposed to.