Half-Life: Opposing Force

Your mission is to eliminate Gordon Freeman. But upon arrival at the assignment location, circumstances separate you from the main group. You come face to face with the most dangerous alien race that has come to Earth after Freeman shattered the boundary between two worlds – the human world and Zen. You realize that the enemy is not some scientist, but a ruthless alien race, and the assignment has turned into a true bloodbath from which you must urgently escape...