Surface Invaders

By Wave Propagation for Ludum Dare 29

Download Game (ZIP) | Download Source (ZIP)
Shoot all surface invaders to get to the next round. If you hit, you will earn time. But if you miss, you will lose time. The more rounds you play without losing, the faster they will run. If your time runs out, you will lose.
To walk, use your WASD-keys and mouse. To shoot, press your left mouse button. You need to press once per shot.
You will require Java 7 or later to run it.
Note: The game has sound, but keep it low and increase over time. It might be too loud. I couldn't control that, for some reason.
The game engine is my own creation. It is called JOGE (short for Java Open Game Engine) and is software rendered, using the Java2D API. Its source code can be found at GitHub.