Hi,
this game is great! I love the simplicity of the controls, which still makes for a challenge. The letters also feel pretty accurate, you seem to have experience with them :) The visuals are simple, but they just work! Also, the sound effects and the music are an excellent choice (the sound of a popping balloon, instead of some descending notes, encourages me more to retry getting the letter to my pen-pal).
Keep up the good work!
-Remi