Defeat Last Boss Easy!

The last boss (Sheridan) is annoying because there are "crawlers", huge crab-like creatures thrown into the equation. But there is a trick, where there is a sweet spot and the crawlers and the boss can't touch you at all, and you never run out of ammo.

 

You will have to do this quickly or the boss will move to position and attack you. As soon as you enter the   arena, sprint to the ammo crate on your left. Tap RB only once to raise the terrain underneath the ammo crate, (anymore will slow you down) and jump up on TOP of the crate.  The boss should be a distance away. If he is really close (like almost on top of you) then you have been too slow. Reload and start again if this is the case.

 

Once you are on top of the crate, shoot the glowing parts on him and ALL the tower spikes around (about 5 of them) to reduce his health. The boss should be stomping the ground and the crawlers not spawning near you. Do not leave the crate and continue reloading and shooting. As you are on top of the crate, you will never run out of ammo. I finished him off in about five minutes with this method.