Alien Brigade is a side-scrolling shooter where you must stop aliens from brainwashing soldiers and civilians to take over the world. The game features five levels, each with a different objective, such as saving civilians or destroying alien installations. Throughout the levels, you'll encounter various enemies, including aliens, brainwashed people, tanks, helicopters, and more.
The gameplay involves shooting enemies to earn rewards, such as extra ammo, better weapons, or increased health. However, if you're not quick enough, you'll take damage, which will slowly decrease your health over time. Your goal is to survive and complete each level without running out of health, as the game ends when your health is depleted.