Clever idea, but almost impossible to play with keyboard, as all the keys look the same, especially at that speed. Gave it a go with the controller, since there are fewer buttons (some of which are colored) in a variety of shapes. Alas, it was still much too fast (in my experience).
You might consider either having them fly across the screen slower at the start, and increase speed as the game goes on, giving the player a sort of 'warm-up' period. Also, having ease to a stop with interpolation would make for a more visually pleasant experience.
Otherwise, you're off to a good start. Fine work, and good luck! :D