Fun game! I liked that there are visual cues and sound cues and that one can assign any key to play the game. It is really accessible to a varied range of players. If you are interesting on expanding the game, it would be interesting to add levels with specific goals to achieve each level. In the earlier levels the game would be easier, with simple and short sequence of tones, and later levels the sequences would get longer, more complex,  faster. Maybe each round instead of one new tone,  two or three would be added at once. Anyway, good job!