This solve was done with one player and not tested with two players.
Examine crashed spacecraft. Pickup "first aid", "navigator" and "laser gun" from the space craft.
Go right and get rid of three aliens. Talk with wounded alien. Use "first aid" on alien (you'll get "laser cutter"). Go back to the spacecraft, and then proceed up to the river. Kill three aliens.
Go up aside the river until you reach the waterfall (kill two aliens). Pickup the "pickaxe" from the floor (alien that escaped by teleportation left it). Go right then down (get rid of the aliens) then proceed right to the next zone.
Proceed right then go down. You'll come to the spacecraft's. Talk to guy that works there. Exchange "navigator" for "supply card".
Go back to the place where you've killed three aliens. Enter the river and swim across to the other side. Get rid of two aliens then proceed up to the next zone.
Go up to the mining place (place protected with electric fence). Collect red "minerals" from the boxes on the left side. Go left to the generator.
Throw red "minerals" into the hole on generator. Kill two people that attack you. Go back to the mining place and kill three aliens.
Enter the mining place and talk to the people inside (you'll get "book" and "ID card"). Go left to the generator, then up and try to open buildings door with the "supply card". Go back to the mining place and talk to the human which sent you for help (you'll get "door card"). Go back to the door and open it with "door card". Enter inside.
Recharge your shield on the recharger. (Here's where you should come to recharge your shield if you run out of shield). Go back to the river, swim across then go up to the waterfall. Enter the cave under the waterfall.
Go up and kill four aliens. Turn left on second turning. Proceed until you get to the power supply unit (get rid of the aliens). Cut the wire on power supply unit with "laser cutter". Go back then down then turn left. Kill the guard alien and cut wire on second power supply.
Talk to the alien you've saved (Harrawie). Then follow him out of cave. Follow him again to the next zone. Kill two aliens. Talk to Harrawie.
Get rid of the incoming aliens. Talk again to the Harrawie. Pick up the "metal stick" he drops when he teleport himself. Get rid of the aliens.
Examine the bushes on the other side of the muddy water then shoot them down. Use "metal stick" to open the door to the hidden place. Search around and you'll find "empty box" and "empty can"
Go back to the place for entering to the river (and where you first killed 3 aliens). Fill up "empty can" with water on that place. Go up to the cave. Proceed up as far as you can then turn left. Proceed left then down to the fire.
Examine fire then use "full can" on it. Proceed left and get rid of the aliens. Search around and you'll found "gun powder", pick it up with "empty box". Find the detonator and make the "bomb" combining it with "gun powder". Go back to the river, swim to the other side then proceed to the room with recharger.
Examine terminal. Talk with the guy sitting on the chair (come from the upper side of the desk). Examine the door (upper door). Talk again to the guy. Give him ID card. Recharge your shield and enter the military complex (upper door). Go right and check the door on the bottom wall (try it several times). Go up and enter the building.
Go to the room on the left and give a "book" to the guy sitting on the bar. (You'll get "locker card"). Go into the upper room and use "locker card" on the left locker (upper wall). (You'll get "officer uniform"). Exit from the building and go to the door on bottom wall. Enter training camp.
Go down and pick up "empty shell" near the weapon (several guys working on it). Go right and enter the depot room. Talk to the guy working inside. Exchange uniform for "gas mask". Pick up "full bottle" from the boxes on the right. Give "full bottle" to the drunken man (guy sitting on the floor and drinking). Exit from the depot room, exit from the training camp.
Go left then up to the building with ventilation. Examine terminal closest to the building (attached to the wall). That will open some door. Go left to the next zone. Get rid of all humans inside this zone.
Inside a smaller part (left down part of the zone) is place where you can fill "empty shell". (You'll get "full shell"). Go back to the building with ventilation and use "full shell" on ventilation opening. Wait a while and the door will open. Kill all the guys around before they attack you.
Use "gas mask" to enter the building. Examine bodies on the floor. Use teleport to get on the bottom floor. Examine terminals. Pick up "acid" and "pills" from opened containers. Go up with the teleport and exit from building. Go to the recharger and recharge your shield.
Go to the depot room and give "pills" to the drunken man. Show him the "supply card" or any other card you have. Follow him outside the depot, outside training camp and then enter after him to the third building. Pick up the "priority card" he puts on the desk. Give him the "supply card" and exit from the building. You will be captured (automatic sequence).
Inside the jail use "acid" on the panel (right upper corner of the room). Enter to the reactor through opening. Walk left and wait on first crossroad for electricity to pass up. Go after it and wait on crossroad for electricity to pass right (watch on up-down electricity).
Go left then up (after electricity pass up or down). Go left to the next zone. Go left then down till crossroad. Wait for electricity to go left. Go left after it. Proceed left till second crossroad. Wait for electricity to go up then go up right after it. Turn right as soon as you can then proceed right to the next zone.
On the first crossroad wait for electricity to pass then proceed right. Then up and proceed up (when there is no electricity) and you'll reach to the wall. Examine the wall. Use pickaxe on the wall. Examine the canyon edges. Jump into the river. You'll come out in the river near the waterfall. Exit from the river and go to the crashed spacecraft. Pickup the "small gun".
Go up then right to the place where guy was fixing the spacecraft.(12.) Go down to the building wall and use "bomb" on the entrance. Pickup "shrapnel" from the floor. Enter the building. Kill the guy that works on terminal. Pickup laser gun from his hand. Examine terminal. (That will activate the teleport).
Refuel your weapon from the locker (on the left wall above the teleport). Use the teleport. Get rid of the guy behind the terminal. And wait for other guy to return with teleport. Get rid of him too. Go left and enter to the small room on left.
Pickup the "screwdriver" from the desk. Go back to the terminal under the teleport and activate teleport on it. Go to the room on right and use "screwdriver" to open the entrance to the sewers (top left place in the room). Enter the sewers.
When you enter through the air conditioning duct you are at the position S (map1). Go to position 1 (map1) and pull the plug. Return back to the start room and go left to position 2 (map1) pull the plug.
Proceed in zoneC through position C1 (map1). Now you are at position C1 (map3). Go left and turn down on first turning, proceed left, then turn back up, proceed left to the position 3 (map3) and pull the plug. Return back to the position C1 (map3) the same way you've came and proceed back to zoneA.
Now you are again in the position C1 (map1). From there proceed left and return to position 1 (map1) the same way you came here. Pull the plug. Go down and turn left on second turning, go left then up as much as you can then again left to the position B1 (map1). Enter zoneB. Now you are at the position B1 (map2). Go left then turn down then again left and proceed left to the position 4 (map2). Pull the plug.
Go up to the position 5 (map2). Pull the plug. Return the same way to the position B1 (map2). Return to zoneA. Now you are again at the position B1 (map1). Go right as much as you can, then turn down and on first turning turn left. Go to the position C2 (map1). Enter zoneC. Now you are at the position C2 (map3).
Go left then down and pull the plug on position 6 (map3). Go back up then left then turn up and pull the plug on position 7 (map3). (On the left machine). Go back to room at position 6 (map3) then proceed left to position 8 (map3). Pull the plug. Now return to position 7 (map3) the same way you've come and again pull the same plug.
Now go down and turn left on first turning and proceed left. Turn down on second turning and go to position 9 (map3). Pull the plug. Go up to position E (map3). Use the screwdriver. Enter the hole.
Pickup the "crowbar" from the box on the floor. Open the door and go to the teleport. Use the teleport. Go down to the big door. Examine door. Open the door with "crowbar". Enter to the research complex.
Go down then left. Kill the guy that stays in front of the building playing games. Pickup the "locker card" he drops. Go right and enter the central building.
Examine terminal on the right wall. Go to the bottom room and open locker on upper wall with "locker card" you've just picked up. Take "ID card" and "lamp" from the locker. Go to the left room and clean your body on the cleaner (upper wall).
Go fasts to the building where you've kill the guy and took his ID card. Use "ID card" to open the door and enter inside. Go down. If door doesn't open go back to the cleaner and then return fast (before you contaminate yourself again). Go down through the door. Talk with guy working on terminal. Kill them all inside that room. Pickup the "door card" from the floor (guy you've talk to has dropped it). Pick up the "hand scanner" and "empty syringe" from the desks in the center of the room.
Work on the terminal on the right side of the frozen alien. Use "hand scanner" to examine alien body on the desk. Go left to the next room. Go down to the door. Use "door card" to open the door. Enter to the room. Kill the guy inside that room. Examine the desk he was working on. Fill "empty syringe" with trimmin serum (the one on the right side). (You'll get "full syringe").
Go back to the room with aliens and use "full syringe" on one of them. Go back to the room with serums and fill "empty syringe" with the same serum again. Go back to the room with alien and use "full syringe" on the other alien. Talk with him and he'll give you the "bracelet".
Go to the room on left and work on big terminal (top left). Go down to the room with serums. Examine the floor under the box you just lifted up. Use "lamp" to see what's inside.
Go to the desk and fill "empty syringe" with other serum (the one on the left side). (You'll get "full syringe"). Examine body of dead guy and you'll get his "ID card". Exit from the building. Go right to the building on the right side of research complex.
Use "ID card" to enter the building. Use the "ID card" (the last one you've collected) on the terminal above to open the central door. Enter the room on the right and kill everybody inside. Sit on the terminal and examine it. Go through lower door on the right side of the room.
Get the "cable" from the locker. Reload your weapon from the other locker. Return to previous room and use cable on the other door (the upper one on the same wall). Use "shrapnel" on the cable to block lower door and open the upper one. Enter the upper room. Kill the guy (the blue one). And talk to the other one (works on terminal). Use "full syringe" on him. Open the locker and collect the "control box" from it. Go away and when he attacks you kill him and get the "priority card" from his pocket. Exit from the building and go to the underground complex. (105.)
Go to the right room and open the door with "priority card". Go up through the door and open the other door with the other "priority card". Go up to next room. Talk to the guy sitting in the chair and working on terminal. Kill him when he attacks you. Examine terminal on the right side of the room then use the teleport.
Kill all guys in this room then go to the recharger. Collect the "power gun" from the locker and "hologram". Examine both upper terminals (one with chair and one on the right side of the chair). Exit the room through the door.
Kill everybody around. Then go right to next zone. Kill everybody there too. Return back to the room with recharger and recharge your shield. Go outside and proceed up between mountain walls to the next zone.
This part of the game will play automatically, so all you need to do is to follow the story.
Now you are in the cave with two barriers and one guard in front of them. Collect the "bomb" from the locker on the bottom wall then go right and exit from cave. Look up if you like then go down to the next zone. Then right to next zone. Place the "bomb" on the door on the right. Enter the building. Go right and kill everybody in this room.
Sit down on both terminals to open two doors. Go to down the next room. Proceed down and kill everybody in this corridor. Proceed down through the door to the next room. Kill everybody inside. Use recharger and examine lockers to reload your weapon. Go back to the room with two terminals.
Proceed up through door to the next room. Kill everybody in this corridor. Go to the top right edge of this corridor. (Kill everybody on your way). (Now is a good time to go back and recharge your shield if you need it.) Enter through the door on the right side. Kill everybody in this room.
Activate teleport on the terminal on the right side of the room. Examine dead bodies and you'll find a "lift card". Go back to the room with terminals. (Be careful on your way back).
Proceed down to the room with recharger. (Recharge your shield and refuel your weapon from the lockers). Exit from the room and go right, then up then again right. Enter the room on the right side.
Kill everybody inside. Sit on the chair in front of the terminal to open the door. Exit from the room through the same door you've come in. Go left then down. Enter through the door on the right side. Kill the guy inside. (at this point you should have full shield and full weapon, otherwise go to the recharger room then return).
Use the list card on the left teleport. Kill everybody inside this room. Then open the door with terminal on the right wall. Go up through the door. Kill everybody in this room. Go left to the next room. Open the door on terminal nearest to the door. Kill everybody in this room. Then collect the "computer key" from the locker on the left.
Go back to previous room. Proceed up through the door. Kill everybody in this corridor. Then go to the room on the right side of the corridor. Kill everybody in this room then open the door on the central terminal. Return back to the corridor.
Go up then right then down through the door. Kill the guy inside. Then proceed right. Kill everybody there. Proceed up then ether left or right. (Kill everybody on your way.) Carefully proceed up and stop before guarding weapons kill's you.
Use "hologram" in the corridor near to the weapons. (You'll see the use icon on panel.) Enter through the door on upper wall. Kill everybody inside this room. Examine terminal on the upper wall. Then use "computer key" on it.
That's it. The rest will be played automatically. Congradulations!