Alien Brigade is a side-scrolling shooter where aliens have taken over Earth, brainwashing both soldiers and civilians to take over the world. Your goal is to stop them and save humanity. On each of the five levels, you'll have a different objective to complete, such as saving civilians and destroying alien installations.
The game features various enemies, including brainwashed people, aliens, tanks, helicopters, and more. Shooting these enemies will reward you with bonus items like additional ammo, powerful weapons, or increased health. However, if you don't shoot fast enough, you'll lose health, which will slowly decrease over time. The game ends when your health runs out.