Excellent little game, very intelligent and brain teasing, it's a good exercise for cognition.
I didn't like the lounge music played throughout the game too much at first, but it eventually grew on me, and the graphics are also pretty polished, with good looking menus, play fields and all other stuff.
I really like this kind of puzzle gameplay, in which you can discover the solution deductively, rather than through trial and error. Another cool thing is that this concept presents some pretty simple, yet cool mathematical properties, including the fact that for each setup of numbers around the board, there exists a single picture (or none) that correspond to that setup. The first stages are ridiculously easy, but after them, the difficulty scales up almost perfectly.
I like how the player's progress is measured in an RPG fashion, with "level ups" being granted after a certain amount of EXP is gathered. There are also the "super power badges", which add a "boost" to EXP and gold, and I love how the looks of the game are highly customizable with unlockable themes and features which are made available by clearing stages, then bought.
To sum it up, this is a pretty complete little puzzle game, and it plays pretty nicely too.