Ah the good ol' genre..
A very nice memorizing game, blending the time trial to make things a bit more challanging. Might want to consider a 'master gardener' mode where a shape of unimaginable complexity quite like those in the later levels, is given for unlimited time to recreate, for higher rewards of course.
Just one thing bothering me- you can't slap extreme titles without upholding such standarts. for instance: EXTREME ironing did it right.