Surviving the raid at the farmhouse
An intermission sequence will start when you are escorting Ashley across a bridge. A large crowd shows up and you will run into a farmhouse. After the sequence ends and you are inside the house with Lou, push the bookcases in front of the windows and go to the bottom of the staircase. Using the shotgun is recommended, but the pistol works fine. Once they are able to gain entrance to the house, aim high and fire until they are all knocked down. Then, reload and repeat until Lou tells you to head up stairs. When you do this, go over to the windows and knock down the ladders. After that is done, go to the edge of the stairs and kill everyone that is coming up Grenades work the best for this. After they are taken care of, rush back to the windows and knock down the ladders once again. Repeat this until the sequence plays when they retreat.
Once in the farmhouse, collect all the items while pushing the shelves against the windows. Stand in the corner by the stairs with Luis and fire until he tells you to go upstairs. Once up, stand in northwest corner (when facing down the stairs), and concentrate on firing in the direction of the stairs and pushing down the two ladders in that corner so that you do not become surrounded.
Because the raid continues until you kill a certain number, block two windows and shoot out the third until the enemies break in. Then, block the third window and deal with the other two. This allows you to get several kills in before it starts getting hectic.