Fans of Sudoku are likely to fall in love with Circles pretty quickly. Like the popular commuter's past-time, Circles is very much inherent with the basic principles of maths. By rotating wheels of four numbers, your objective is to dominate the sum of yellow numbers, with your blue numbers. A simple example might see the rotation of three blues and one yellow, each assigned with the number one. The yellow ball would be eliminated, as its sum total is equal to 1 as opposed to the blue's 3. Make sense? Phew, if you think playing the game is hard - try explaining it.
Other mechanics see each of the balls' sum increased or decreased by one upon elimination of an opponents ball. Here you can be coy, and sacrifice a blue ball to see the yellow's value dramatically decreased. Many levels (especially those above the "Easy" difficulty level) will require deep levels of concentration, with Gold medals awarded to perfect performance, and Silver to basic level clearance.
Circles gameplay is so thought-provoking, it doesn't really matter that its audio is woeful and its presentation hideously basic. Like Sudoku is just a grid of lines, Circles is a simple palette of blue and yellow numbers. Presentation is the side show here though. Circles is all about numbers.
If you're a fan of Sudoku, but fancy a change, there's more than enough here to give Circles a recommendation.