At first I thought "Why isn't it keeping track of my number of moves? Where is the challenge without it?" But I quickly realised it works much better as a relaxed experience, without a constant reminder that you can do better. There's just something serene & satisfying about filling in all boxes, even if it is almost exclusively trial & error. The game is also just the right length, perhaps maybe 2 levels too long I was about to quit at 30 until I saw I was near the end.
The art looks poorly made & inconsistent at first, but it has its own charm (like the constant variation in color). Especially the "Level complete Awesome!!" has a really neat 90's WordArt feel to it. The menu could look more interesting though.
Also, great music & sound effects! I don't think I would've completed the game without it.
Besides some small touches the game is pretty much perfect. I would look up "game juice", this game doesn't <em>need<em> it but it makes pretty much anything more fun. Also, adding some variation to the sound effect via a random pitch shift does wonders.
As it works so well I have to ask, how did you come up with the concept?