Monster Attack is a third-person action shooter and the first game in the Chikyuu Boueigun / Earth Defense Force series. The player takes the role of an EDF (Earth Defence Force) infantry man to single handily battle hordes of giant bugs, robots and alien ships that have invaded Earth, across 30 missions. The game alludes to other EDF forces, but they are never seen.
You choose two weapons for each mission from dozens of various missile launchers, machine guns, flamethrowers and more unique weapons, some faster, more powerful or better suited to the mission at hand than others, are given infinite ammo (though the weapons must still be reloaded after each clip is used up) and are set loose in one of several (usually city-based) fully destructible environments. Players can also mount vehicles such as an air bike, a tank and a helicopter.
The player recovers and increases his maximum health and armour, and unlocks new weapons by picking up power-ups from defeated enemies that spawn in and come at the player by the dozen. The game also features 2-player split-screen cooperative multiplayer.