In the final level, get the Berserker's attention. Berserkers are blind and only go off smell and sound. Lead her all the way back to the very first train car. While she is still on it, immediately run off and press the button to release the car. Have fun watching the train car collapse while the Berserker goes with it.
Taking Berserkers out usually takes two hits with the Hammer Of Dawn. However, if you stick a grenade to them while they are still glowing red, it saves the trouble of aiming again with the Hammer Of Dawn. This is easier with two players, but not too difficult to do solo.
After a hit with the Hammer Of Dawn, immediately hit it with a Torque Bow. It will go down with one bow, just like the Boomers. This is useful when playing in Insane mode where the Berserker sometimes may take four Hammer Of Dawn shots. Also, using a Torque Bow is much safer then trying to tag with a grenade.
Before you try to open the door that Jack has to "rip" that leads into the train car, shoot the fuel tank until black smoke starts to come out of it. After the Berserker appears, go back to the fuel tank. Note: The Berserker needs to be on the same car as the tank or any car behind it. Just throw a grenade under the fuel tank and make sure you are not on the same car. The tank will explode and will detach the car, killing the Berserker and sending the cars and everything on them flying.