When you begin the final battle with General Crowe, make sure you have a lot of grenades and the assault rifle with the grenade launcher equipped. General Crowe will not fight person to person yet. For now, focus on the monsters jumping around. Do not fire the helicopter's rocket launcher. You will need it for when you fight Crowe. Also, use the helicopter to shield yourself from Crowe's machine gun fire. Using the grenades with perfect accuracy, kill the monsters. Get two of them at the same time if possible to save grenade rounds. At some point they will stop dropping down. When this happens, focus on Crowe. After some time of shooting at him, he will jump down and fight you person to person. Avoid his machine gun, as it takes a lot of your health away. It is recommended that you use the speed ability to dodge bullets and hide behind objects to regenerate health. When Crowe gets in front of the door, use the helicopter's rockets. Once Crowe is dead, it is just a walk to the end.