Just too hard...
Even on easy I find if you don't get off to a good start (which is luck really, since the guns are so innaccurate) then the whole game just gets harder and harder. This is not the right structure for a game my friend.
That's my only critique. Everything else is a 10 and is wonderful! You've really taken everybody's suggestions and upgraded it a lot! Great work buddy, this has been a great game series!