Take out the first two gang members and head towards Nacho. He'll close the door he came through, so you're going to have to go through the door to the left, which, naturally, is full of guys with guns. Being in cramped conditions, it shouldn't be too hard to hit them before they cause any damage to you. Go down the stairs and you'll come to a large room with stairs going up. Rush forward past the stairs and take out the guys waiting. Now go up the stairs and take out those gang members, but don't forget the drugs in the lower corner. Keep going until you reach a room which opens out onto a large balcony system. There is health to the left and this is a good place to use blind rage. There will be guys rushing all over the balcony system, so make your way along killing those in the way and on the different levels. When you reach the doorway, take care as there should be a large number of guys there. Once you get up to the top of the stairs, you'll reach a checkpoint.
Keep crouched and take out the guys hanging around the next room and make it to the balcony and up the stairs. Take them out at a distance, and be careful you don't get shot in the back from the higher levels. Once you reach the control room, use wall cover and take out the guys waiting and pick up the health pack if needed. In the next section, be aware of all the oil barrels. If you're standing near one of these and it goes off, it'll be game over. Of course this works both ways. Make your way down the stairs killing those in the way and blowing up barrels. Use blind rage if your health is low and you've already collected the health kit. Collect the drugs at the bottom of the stairs.
Now follow the constricted path, taking cover, crouching and shooting all those that get in the way. Be careful, as this place is littered with barrels as well. Once you've gone across the wooden bridge, you'll reach another checkpoint, and it's almost over. Take out the two guys that are coming towards you. Now there are two snipers at the far end, so either use blind rage, rush towards them and kill them quickly, or take cover and pick them off from afar. Note that the last method doesn't really work, because they have sniper rifles. Provided you're a good shot, rushing at them should kill them before they kill you. Now just use the sniper rifle you picked up to shoot Nacho. It might take a few hits, but do it before he reaches the boat.