I should probably fix these, but then I wouldn't have anything to put here.
There's no way to cancel saving a high score.
When you get a high score, it shows the You Won sheet as well as asking you for your name in a different window.
Changing many of the preferences requires you to make a new game, even if you already have a new game.
Some text and help is probably unclear; Best Times is sometimes called High Scores.
The program is not easy to use with certain Universal Access option (e.g. High Contrast)
The program is only in English
The program uses only color to indicate certain things. I don't know how accessible it is to colorblind people (I've read that red can appear dark, and it mainly needs to contrast red with light gray, so maybe it's not too bad). Turning off colored numbers and/or yellow squares may or may not help.
The uncovered and covered squares can be hard to tell apart at certain angles on my monitor.
If the computer is slow, it will affect how much time it says you took