Great graphics, really fun, and I just love how you put in the various weapons in the game, especially the gatling gun!
I think the enemies look too similar to the wavy grass though. The screen shake also gave me a bit of a headache, lol.
It's also great that you went all the way to do a retro-style score system, but given the players are mashing the shoot button all the time, I was skipping through and submitting scores for "AAA" - suggest using some other key to do the score submission.