Open up with automatic weaponry on the shutters and get a grenade in there when there's enough room created by all the splinters. The Helghast behind the shutters will be trying to do the same to you. Helghan's are just to angry to bother opening windows. Move on through by following the waypoint.
You are about to encounter the toughest yet dumbest enemy units in the game - the Helghan Heavy Weapons Trooper. Ignore him at first, keep moving between cover and kill all the standard Helghan troops nearby and make sure you reload before attacking the big guy. You are meant to shoot him directly in his face which will, quite ridiculously, turn around to shield his face while exposing fuel tanks that he keeps on his back.
You can either take cover behind a pillar and attack his face, or cook a grenade and throw it right at him. This way you won't have to worry about a head shot since the grenade's splash damage will hurt him plenty, and you will save ammunition that you will need to blast him on the incredibly obvious weak spot on his back.
Alternatively you can try running to his rear straight away while he attacks other ISA troops, but the success of this tactic is all down to the random behaviour of your AI team mates.
Follow the waypoint and turn the valve using the incredibly realistic Six-Axis turning mechanism. It's even more like 'being there' isn't it? Carry on following the waypoint down a corridor and up some steps and you will encounter a group of ISA soldiers facing Helghast taking cover.
Cook a grenade for two seconds and lob it at the Helghast and take cover yourself because you are about to get counter attacked by enemy units whose woolly hats make them look even more WWII than usual. Standard enemy units will attack from cover, but when you see ones with woolly hats on you should know that they are willing and able to charge straight at you, swapping between their guns to knives when they get close.
They specialise in back-stabbing, so kill them fast before they get too close or worse, behind you. Those knives cause plenty hurt. Kill 'em all and follow the waypoint.
You'll encounter a metal ramp and, worse still, Helghast the other side of it. Move while crouching and use the ramp as cover then run up it and get hold of a nearby RIFLE and use its long-range accuracy to slaughter the Helghast you'll see far away taking cover behind a wall.
Follow the waypoint and make sure you look left at a junction where the waypoint suggests you should go right and you'll find some Intel. You'll know you are close when you are asked if you would like to call the elevator. It's a rhetorical question, of course, since if you don't call the elevator you won't be progressing any further.
When you exit the elevator you will see the Arc Tower in all its phallic glory. Run across the bridge and meet up with another group of your men and follow the waypoint as a band of brothers. Take cover and kill the Helghast that are hiding behind some air ducts and follow the waypoint and find another piece of Intel in a small room that features a short stairwell. Go up the stairs and prepare for some heavy resistance, but considering you are fighting the Helghast on their home turf what did you expect?
You will need to be ready to shoot at the glowing blue power nodes of the Arc Tower while simultaneously fighting a Helghast counterattack so it's important that you reload your weapon at the right time. Reload, then press the button on the control box. This will cause the Arc Tower to open up panels on its side and expose the blue conduits.