Great shooting game. Use a huge array of weapons, equipment, and abilities to fight off the alien forces and save the human race. Or you can become the bad guys and fight against the humans.
Movement - WASD/Arrow Keys (or Space to jump)
Aiming/Shooting - Mouse
Next/Previous Weapon - Q/E or Shift/Enter
Select specific weapon - Number keys
Use Ability - F/Ctrl
Pause - Esc/P