It's the first time I'm writing a "stay-away-from-this-*bad_word*" review here... but this game needs it like nothing else I've tried so far.
I've bought it for 0,99€ thinking what the hell. The first levels were quite nice - nothing special and pretty far from what I expect from a "music game" at the same time, but still nice. Then I got bored. And then the final levels came. They are ridiculously hard - not challenging, just annoying and badly programmed. I found it impossible to finish the last one, but my masochistic mind told me to do it and get all the achievements. So I tried and I tried, and I tried, and I tried. And suddenly I had to thank the GREAT programmers of this FANTASTIC GAME because hey, you can pause the game and still link these damn notes! What a relief. What a joke.
I finished the game and still got two achievements locked - "500 Notes", "250 Max". So I kept playing this "pause and link" game, making it my worst enemy... And then I found out the game is not saving your achievement progress. You have to launch it and keep playing it until you unlock these achievements. And guess what? Even they are bugged (I got it after over 600 notes were placed and over 300 max length chains detonated)...
So yeah, I wasted my time on this game as it ironically became a challenge to me and activated my "achievement wh*** rage mode". Don't let it do the same to you. :)