Thanks so much for playing and reviewing my game! It means a lot.
Also a musician - I agree, and it used to be even harder - you had to play the melody perfectly each time. Imagine! As you noted, the melody standing out is definitely an issue and I should have had more sustain or something, even though I wanted part of the difficulty curve to involve the beat becoming more complex so you'd have to focus harder on the pitches. I tried to make it easy for the player to remember the rhythm by starting the playback on beat 1, but I forgot to implement it correctly for the harder two modes... oops.
I'll check out your game!