When you reach General RAAM at the end of the last Act, he will have a Gatlin type gun and be surrounded by the Bird Locust. There will also be flying Locusts attacking from the side of the train ( just ignore them). You can only hurt General RAAM when the Bird Locusts leaves him and goes for you. Stay in the light or the birds can kill you. When you start fighting him, hide behind the first rectangular block that is directly in front of the doors you came from. He will start walking towards you and shoot at you. When the birds leave him, start shooting. Eventually he will get directly in front of where you are hiding. When he does, run around him and hide on the other side of the platform. Stay in the light as you run and hide,then continue shooting him until he dies.
Before facing General RAAM, make sure you have the Longshot (sniper rifle) and Torque Bow with full ammo--you can get the Longshot in the car before fighting RAAM, and ammo is also found there. When you fight RAAM, first tell Dom to cease fire so that he stays in safe. Apparently this stops RAAM from coming towards you. The only way you can hurt RAAM is when the Kryll (the bats around him) are not shielding him. Use the Torque Bow to get rid of the shielding Kryll, then take out the Longshot and give RAAM a lovely headshot. It is very important to reload rapidly. If you are lucky and can get a couple of active reloads, you can headshot RAAM twice before the Kryll shield him. Continue this process until RAAM is dead.
To defeat RAAM at the end of the game, simply duck behind the first blockade (the one you start at) while using the sniper rifle to shoot RAAM from a distance. Stay ducked until he gets to the other side of the block, then blind shoot whenever he sends the Krill guarding him to attack you. He is unable to shoot you at this spot. Just continue until he is dead. Also, do not worry about saving your teammate or shooting the Reavers as they are only distractions.
Get General RAAM off the Gatlin gun. When he starts walking towards you, let Dominic get his attention while you run towards the Gatlin gun and shoot him with it. This should kill him in seconds. Note: This is easier in co-op mode.