Head down the tunnel to the right, then through the opening door and into the lift. Ride it up, then go outside and right. Continue going round until you reach the entrance to the Generator Shed. Head into it, then follow the corridor round to the left until you come to a glass window. Shoot the glass with a grenade, then jump through the window to the little pad on the left (you can make it, it just requires some precise jumping) and then fall down to the floor. This way you can get down without loosing any health. Pull the four levers, then wait for the doors to open and the power to come back on. When this happens, go through said doors and go up the stairs, then go right. Follow the corridor round again, then when you get to the glass window through a flare somewhere in the room - a door in the far corner, which was previously locked, is now open. Go through and follow the ledge round again, but now you can ride the lift at the end up as it is now powered. At the top, go along the pathway and crouch to through the hole at the end. In this room is a Smartgun, which I suggest you use, and on the easier levels there's a Medikit, although really you shouldn't need it by this point. Exit the room and go along the ledge, down the lift etc. until you exit the Generator Shed. After doing so, head right and you should emerge in an area full of bars, homesteads, etc. Head right to the main building, and pull down on the lever to the left of the large door. It will open. Go through, then go right. Follow the corridor round until you come to a door - it's locked. Instead, look right and you should see a vent on the floor - crouch and head through it, then go up the steps, round and through the other vent. You'll emerge in a large room with four barrels in it. There should be an alien nearby, either in the room, or directly behind the doors to your right. After it's dead, proceed through said doors and follow the corridor round to the water-flooded area. Take the right and ride the lift up to the top level. Get off, continue down the corridor and then turn right. Head up the stairs and into the Ops Room. Pull down on the five switches. Head out the opposite door to the one you came in by, then head down the stairs, and take the next right. Go down the steps, then look right. You should be able to see a Smartgun. Collect it, then continue down the stairs to level 2. I'd recommend you save it until the end, when you'll really need it. Follow the corridor round until you reach a large room that lights up as you enter it. Kill the alien that appears then head through the doors on the far right. In this room, collect the Flamethrower at the far end then proceed through the doors on the left. Go to the end of the next room and go through the doors, armed with the Flamethrower. Fry the face-huggers, then collect the bonuses and the Bypass kit. Now, head out of the room, through the Med-lab, round the corridor and into the room with the sets of stairs. Now, sticking to the left-hand wall, fall down to the next level (i.e. fall down the broken stairs). Now turn around and go down the steps, then right when you reach the large water flooded intersection. Follow the corridor round and go through the doors. In the far left hand corner there's a series of pipes which get progressively higher. Jump onto the lowest one then work your way up to the top, before entering the vent on the left. When you emerge in the next room, ignore the steps to your right and head left, then go down the steps and through the next vent into the corridor. From here go left, then when you reach the main door exit to go outside. Go down to the end of the "street", then go right. Keep going round until you reach the main gate, and it will open automatically. Now simply keep heading down the small valley outside, armed with the Smartgun you picked up earlier, killing any aliens you meet. Approach the APC at the end to finish the level