Always been a huge fan of these sorts of puzzles, and this one I've just fallen in love with. Also, it seems to be pretty replayable as the 'differences', or at least a select few, seem to be randomly generated.
Very cool.
Little slow, but good "Looking" game. Not sure why anyone would purchase the basic gun when the machine gun is so much better. Not enough options, upgrades, etc to make this game more than a one shot time sink.