I loved it. Difficult where i expected it to be, at other times really relaxing. Music goes with it well, the concept is something not chewed over 40000M+times, and it's done fairly well.
The only thing i would like to suggest for anything similar in the future is this:
Sometimes, it felt like i lost just because the thin line between one magnet and the next was so small there was no way to judge when it would switch. I personally think it'd be a better idea to provide players with a "switch magnet" button, which would simply move control from one magnet to the next or previous one on screen. This would be especially helpful in Yellow and Blue levels - the purple ones usually make a lot more sense :D
All in all, great game. Thoroughly enjoyed it.