I liked it very much. Also, in addition to Alegene's suggestion for background music, I would like a possibility to change the colortheme. If not by color picker, some preselected themes would do it.

is a beautifully done game, but needs a kind of background sound, a violin of some kind? also, you can block the levels util we can win them, that will easily make the game a lot more interesting, good luck.

Fun, would be nice if there was a way to see which ones I completed, or if they weren't all unlocked at the start, just to give a sense of progression

A very fun and well made puzzle game

This game is very good! It's a simple concept, but it's well executed, and fun. My biggest complain is with the colour scheme. I think that the game would benefit greatly from a different scheme, with two different, contrasting colors. Complementary colors (red-green, blue-orange, yellow-purple) or black-and-white are classics for this, and with good reason. They allow the player to get plenty of information at a glance, making everything stand out and be less monotonous, without becoming garish.

Well, and some background music would be nice, too.

Despite that, however, this game is fun and addictive, and I feel that, with those changes, plus a few more levels (or perhaps changing from hand made levels to procedurally generated ones, Loops of Zen-style) it could become rather popular.