It looks really polished and professional, but there's a few issues. Firstly, it's quite difficult to guess capital cities. I got 'Lome' and guessed it purely by chance. Maybe some sort of clue may help?
Secondly, it would be good to just be able to use the keyboard. It's annoying to have to use the keyboard and mouse. It could be done with just the keyboard, perhaps having to press the letter once to select and twice to confirm if you want people to be able to change their minds.
Finally, hitting 'try again' should just give me another puzzle, not send me to the main menu. also think that if I get one right it should then just give me another and keep track of how many I can get right in a row.