I like the graphics a lot. For some reason, you can't redo a level that's already been solved. Hmmm.
The fact that there is only 1 solution for each level leads to some interesting analysis. Look at the first image. The top row has 11 & 4 directly in the center. Under it is 4 & 11. If the top 11 pairs with the 4 below it or to its right, then the other 11 must pair with the 4 that's left or above it. But because there's only 1 solution, we know that those pairings would lead to two possible solutions. Therefore, that top 11 must pair with the 4 on its left.