Very interesting concept. I kept finding something new in this. After several rounds of 4x4, I realized it is really just a system of equations, so the next few levels were really easy to solve after being plucked into a matrix and calculating kernel. However, on 5x5 grids the level generation algorithm probably changed, as the matrix started to have very strange kernel. Then I found a new strategy, which seems to work on almost every level. In each turn, you just tap the highest number tile out of all the tiles which are neighboring with the highest numbers on the grid. If there are more same numbers, you just pick the one that has the biggest sum of the tiles affected. Since you know that, it gets quite monotonous and easy. I finished the "story" mode, or first 100 levels, and got bored after that. The help option was not of much use at the later levels, as you know you will press each tile at least once anyway. Also, the numbers really should be visually distinct. It would hurt the visual feel of the game a bit, but would help the experience quite a lot. Just a specific color for each number would be enough (think Minesweeper).
Game has a nice challenge. There's an easy way to reset the game without seeing an alert for "try again." Where hints can be delivered for just a 30 second ad. Very pleased!
Very nice gameplay, but boring safe contents ruin the game.
Perfect for getting the brain in gear!
Not very challenging, and not that great from 111%.