F keys are bad.
It's not a good idea to have F keys (F1, F2, F3), you should choose something else. Good choices are Ctrl, Shift, Enter, Alt, etc. The reason why F keys are bad is because it won't necessarily work for everyone. It's possible that these keys won't be recognize on some keyboards. There are also many keyboards that work differently, which mean that pressing a certain F key may result in doing something you don't want to.
On my keyboard, F1 decreases the brightness and F2 increases it. As for F3, it actually does the exclusive Mac feature called "Exposé".
It's a nice game though. Too bad I can't pause the words and letters.