From your comments, I think I understand why the "choose an octave" thing was such a hard choice, but I think what you settled on was quite possibly the least intuitive option for me. Even once I thought I understood how it worked, it kept jumping around on me every time I wanted to try another note. It was frustrating enough that I wouldn't come back to the game over it, because I can't even practice with it until I do get the hang of it with the "one puzzle a day" limitation. And most of the comments support that it wasn't intuitive for the majority of people.

Virtually everyone has at least some relative pitch, enough to know "the next note should be right/left of the last one." Moving the whole octave, and only really showing that with the highlights on a tiny keyboard above is just confusing.

I'm one of those people who virtually never puts my phone in landscape mode, but I would rather unlock landscape mode for one puzzle a day so you could display the full range of applicable keys for the featured section of the song than try it the current way again.