One other thing I forgot to mention - the man sinks into the ground sometimes when jumping - this is a relatively common bug and shouldn't be too difficult to solve :-)

It'd be good if the lines could manifest themselves as lines rather than a series of dots - you could achieve this by drawing a line between the previously placed dot and the new one whenever one is drawn.

It'd be nice to have a blank space available between 9 and 0 - if you click on a square by accident there's no way to get rid of the number at present which could be quite confusing!