Nice attempt...
... but it didn't quite cut it for me. Games that use arrows usually go in the order
%u2190%u2193%u2191%u2192 and not %u2190%u2191%u2193%u2192 otherwise things can get kinda confusing for people who have played similar games. Of course that doesn't matter when the game is so easy to cheat at. It could also do with some indicator on the screen of the exact time to hit the button instead of just being able to hit the note for the entire time it is visible. With indication of timing you could also add different score values for accuracy like 0 for miss, 50 for barely, 100 for average 200 for good and 300 for perfect. If the player presses a button when there is no arrow you should subtract some points from their score as well as breaking their combo, this will stop button mashing.