Start the game with a joke, I like that!
Well, I'm kind of proud that when I was asked to type a word starting with J and an X inside I came up with JUXTAPOSITION. :D But couldn't remember any word starting with K and having an M. Well, native speakers definitely have some advantage here. But I actually had a lot of fun with your game, well done!
Out of curiosity: what dictionary source do you use? It seems names are not recognised (or I did type them wrong all the time.)
[Edit]
Only two minor complaints I forgot to mention: pressing space after your shift does nothing for me, and the initial message you get from your instructor was gone too fast for me so I couldn't read it the first time I played.