Tetris is brilliant and everything, but it has its drawbacks. For a start it only relies on shape recognition and the ability to react fast to a stream of those shapes - there's nowt more to it than that really. And secondly, there's the very real concern that people suffering from apperceptive agnosia (that's an inability to distinguish visual shapes) just aren't able to play it.

Yes, I had to look up that condition - I'd never heard of it either. And yes, I'd love to watch a person suffering from it playing Tetris.

Anyway, there's clearly room for a game that evolves the game of Tetris into something a bit different. And that's where KooZac comes in. For the mysteriously titled game combines a sort of Tetris puzzler with sudoku to make a game that has you forming maths sums from falling blocks.

Those adverse to maths needn't worry though - KooZac requires no more arithmatic skills than being able to add up to 9. The challenge is in being able to add up to 9 extremely quickly.

There are three ways to play the game - a Relaxed mode, where an endless level feeds you numbered blocks until you eventually crumble under the pressure; the Classic game, which has 12 levels and criteria to fulfil in order to unlock each new one; and Expert mode, which introduces a new scoring system and a faster pace of block falling.

Essentially, though, there's not much difference between them all. The basic game stays the same throughout.

The way it goes is that blocks fall one at a time from the top of the screen, each with a number on the front. There's also a second number in the top right of the screen, which changes every time a new block falls.

What you have to do is make that specified number by stacking up a row of the falling numbered blocks. If you have to make the number 7 and you put a 4 on top of a 3, you're successful and those two blocks are wiped from the board.

Both Classic and Expert work by giving you criteria to meet in order to progress. So you might have to form six x2 combos, three x3 ones and one x4 one. These relate to the number of blocks you use to make the required number. So instead of using 4 and 3 to make 7 and form a x2 combo, you could use, say, 2, 1 and 4 to make a more valuable x3 one.

And that's really KooZac explained. It's a simple idea and one that doesn't use any power-ups or other fancy extras (except for bombs that you can collect and use to clear rows in Expert mode). Of course, the simplest puzzle games are often the best and KooZac is definitely very addictive.

It's a well put together game, but for a couple of small problems. Firstly, a level is deemed over once a 'tension bar' at the bottom of the screen fills, which is essentially when you've allowed 25 blocks to fill the screen.

However, even with 25 blocks, only a third of the game screen is filled, meaning you could still possibly salvage the game and succeed were you given the chance.

It's easy to forget the bar, think you're doing well then lose it because you've allowed a few more blocks to drop. Why they haven't just used the tried-and-tested Tetris idea of letting blocks stack up to the very top of the screen, we're not sure.

Also, the speed that blocks fall at feels a bit random. That means the difficulty curve of the game, especially in the Classic mode, is inconsistent. When blocks are going slowly it's very easy, but they quickly speed up to a pace that most will struggle with.

If the sound of Tetris crossed with sudoku sounds good to you, you'll undoubtedly enjoy KooZac. Unfortunately it's just not quite as good as it feels like it could have been, given the solid premise behind it.

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