Interesting mechanic, good looking game, really minimallistic. Not bad. Although, could be better to increase a little bit the difficulty,  like increasing the rate of lines that appears, maybe no so much at the same time, but one after another (this could happen on the green level, because is there where i began to feel that the difficulty wasn´t high enough).

Something else, and this has to be with the music itself. I don´t know how much you can change this but, the music need variation. I understand that, if the levels are completed fast, you wouldn´t notice it, but for someone that has touched the lines once, or more, will otice that the music feels repetitive, maybe with a secon section where change the instruments, or chords, or remove some instruments for certain number of measures, just to contrast a little, and could be more digestive. Some things has to rest a bit, to return stronger than ever.