When someone's trust is in the orange and they will not do anything for you, enter first person mode and aim the gun at their head for three seconds. They will now do things for you without good trust.

Wait about one minute at the main menu to view a longer, uncut television trailer for the game.

Use the following trick to get a doctor in the same room with you during your battle with the second giant Thing. Walk to the large garage door. Get the doctor close to the door as well. Then, tell him to not follow you anymore. Push him as close to the door as possible; and close enough to you that when you flip the switch to open the door he will not move. Before you flip the switch, tell him to follow you again. Flip the switch and when you are shown in the locked room with the second giant Thing, he should be beside you. Use him to heal you during the fight with the Thing.
The following trick requires Stun Grenades (found in the back of the room with Boss 3), Blood Test Kit (found in the same room), and the Grenade Launcher (in the save room down the hall from Boss 3). Starting after third Boss fight (hanging tentacle monster), backtrack your way out of the weapons lab, back up the air vent, and to the "mine" elevator. As soon as you reach the surface, strafe left, and equip both the Grenade Launcher and Stun Grenades. If you step forward at all, it triggers an intermission sequence you have to die and start the level over. Enter first person mode and aim up the corridor, parallel with the bottom of the last metal wall panel. Launch a grenade and quickly walk forward. The intermission sequence will trigger, but Whitley will stand still instead of running off. Now, quickly run ahead of him (preferably block his path to slow him down) and use the Blood Test Kit. He now trusts you enough to follow orders. Order him to follow you (otherwise he walks around the corner triggering guards to attack) and give him a weapon. You have now backup. He only lasts a brief amount of time, and will disappear roughly halfway up the snow corridor, which appears scripted. However, every bit of backup firepower helps in that spot.

In the last level where you have to find Whitley as an objective, as you stand in the elevator strafe left and launch a grenade just outside the opening. If done correctly, you can bring Whitley with you to help kill all the troopers. Note: You have to give him some weaponry.

In the level where you must find Faraday, do not hit the switches until you have met the medic downstairs. Bring him up to the top of the ramps and tell him to stay. Hit the switches and go to find Faraday. Leave, and on your way out, the medic will not have turned. You will get two medics for the remainder of the level.

On the level where you must gain access to the weather station, go to the side of the building to your right. Throw a grenade under the vent and the door will be blown off, allowing access. If you had gone in regularly, Williams would have turned into a Thing. Using this trick will save many medikits for the levels ahead

When you encounter the first Thing Boss, hold Up/Left to run diagonally and you should run under it before it can hit you. This will also aim you directly at the junction box. Immediately start fixing it. As soon as it is almost fixed, hold Right to run through the door. Since he will still keep fixing it as long as you do not release the button, with luck it will be fixed before the Boss attacks for the third time. At the intermission sequence you tend to take off in a random direction, so this may take a few attempts -- save immediately before trying this. If successfully completed, you will lose only about half a bar of health and no ammunition, making the next area much easier.

Go into to his garage. Fix the electrical panel that operates the hoist. Step back towards the middle of the big door. There is an opening between two of the crates. Using your grenade launcher in first person targeting, send in a grenade. If the Thing turns its head toward you, then you have him targeted. Continue sending in grenades until he begins to burn. You can send in a few more if desired for extra fun. Run into the Thing's room and on the far wall from the big door is a switch. Throw the switch and watch as the Thing dies. You will probably take one hit from him.

Run around the Boss in a circle while shooting it with the machine gun. When it is low on health, use the flame thrower to finish it off. If done correctly, you can kill it without being hit. After you kill the Boss, the Thing in the glass in the room will break out, and the door will be opened with a few guards.

This Boss has a sweet spot. If you get directly under it, it will not attack. When you get under it, blast away until its health is in the red, then burn it.

In the level where you first enter the road tunnel, go right to the truck. Blow up the barrel to kill all the little things. You can now either have an engineer fix the lights or not. Follow the left wall back to the door you came in and stop near it. There is a Walker locked up in some boxes. Throw a grenade to blow up the box and let the Walker out. Run back to the truck, or better yet, stand there and watch (if the lights are on). The guards not only get slaughtered, but really wear the Walker down. After he kills the guards, get him to walk around to you (not leaving the general area) then blow up the barrel. If you done correctly, you will kill the walker with ease. Otherwise, torch him.