Instructions are lacking
Firstly, the instructions tab is half-hidden at the bottom of the menu screen so that on first playthrough I didn't even notice it and really struggled to figure out exactly what I was meant to be doing. Then the instructions don't make any reference to the symbols which apparently are also important - if you include a corner which is the right colour but 'wrong' symbol for that colour, the rectangle fails, you lose points and the tile changes. Once I figured out what was going on, I started to quite enjoy it, but frustration at not knowing what was going on for quite some time really coloured my opinion