Minigun Massacre (My first "Game" !!!!)

My game is already uploaded on Gamejolt.com to hopefully get some feedback on how to improve it and what not. This is my first game and it’s 6 days in development. I would really love some feedback on whether this is a great accomplishment for a newbie or not, because I really don’t feel like I’ve learned anything and I’m constantly running into problems on how to control my entities.

Link to the game: http://gamejolt.com/games/shooter/minigun-massacre/37170/ (Press Quickplay or download the game from there).

The game is created with slick2D with Java.