A New Beginning
You'll start off with a short tutorial to get used to the controls. Listen to the Helghast officer and as he instructs. You'll learn the basics of taking cover, using side arms and sights. Take out the enemies and follow your partner to the execution room.
After a brief scene, the story will return to shortly after the conclusion to Killzone 2. You'll once again be taking command of Sergeant Sev and will have Rico by your side. Do as your buddy instructs and kill off the unsuspecting Helghast ahead with a stealth melee attack.
You'll soon meet with the rest of the ISA, who are pinned down in a fire fight. Run up the stairs on the right and take cover. Pop out and use your iron sights to hit each enemy Helghast in the head. Rico and the rest of the soldiers will be able to provide cover fire and take out a good chunk the foes.
You'll arrive at another lone enemy that won't notice your presence. Brutal melee him and move on to the next area. You'll come to a room with a fountain in the middle and guards on all sides. Take out the enemies on the left and take cover behind the fountain. Slowly take down the rest while Rico distracts the rest of the enemies.
In the next area you'll see that there is a valve that needs to be turned in order to open the gate. Take cover on the far right and headshot the Helghast in your way. climb up the stairs and take out the remaining forces at close range. One of them will be carrying a shotgun pistol, which is superior to your current side arm. Switch out for this weapon and move to the valve.
Use the Sixaxis or Move to rotate the valve and open the gate and move on. There will be a turret nearby that is great for mowing down the enemy. Heavy weapons while mounted, such as this gatling gun, will have infinite ammo. If you choose to dismount them they will have a limited amount of ammunition.
Take the gatling gun with you and enter the warehouse ahead. The power and speed of the gatling gun is enough to turn the Helghast into soft butter. If you happen to run out of gatling ammo, switch back to your assault rifle and clean up the rest of the goo. Don't worry about your rifle clip, as there will be plenty to restock on in the next room.
Support Rico in taking out the next wave of bad guys and plant a bomb to blast open the door. Much like the valve from before, turning on bombs requires the use of the Sixaxis or Move motion. More enemies will appear, including some that will try and rush you. Take them down to conclude the first act.