Alien Soldier is a side-scrolling run and gun video game in which the player controls the main character, Epsilon-Eagle, through 25 stages and 31 bosses.
The gameplay has been compared heavily to Gunstar Heroes; however, putting a much larger emphasis on boss fights, and lacking any 2-player option.
Epsilon-Eagle can run, double jump, hover in the air, and use six different types of weapons. Only four can be equipped at any given time, but the player may choose which weapons they would like to equip before the game starts. Each gun has its own ammunition bar which can be replenished; if it's depleted the player will be left with a little firepower.
The player can also perform a dash across the screen, which when at full health, will become a deadly move called "Phoenix Force" that will damage any enemies in its path. There is also a counter move, that if timed properly, will change enemy bullets into health.
Epsilon-Eagle can attack in either fixed-fire or free-moving styles. The first makes him immovable while firing a weapon, instead allowing for quick aiming, while the second allows walking and shooting simultaneously with the sacrifice of directional accuracy.