Its certainly an interesting concept.
The glitches (which everyone else has already mentioned) did sour the experience a bit, especially seeing as those glitches were more 'sources of frustration' than 'sources of amusement'. However, if those were to be fixed, this would be a pretty good game.
However, I'm still not entirely sure what the defence blocks are intended to be used for (are they just intended to be used to get in the way of the giant enemy squares? are they intended to be used as surfaces to bounce shots off so they can hit the giant enemy squares?)