for those of you that can't find the g-man alot in the game, here are a few good tips to find him in certain areas.
1. on the camera in dr. kleiners lab. when barney comes in and says that you stirred up the hive. and then he will turn the camera on. go to the screen and click on it until you see the g-man.
2.when you come to the first part where you come to a little water, after passing a railroad and running from some civil protection guys and jump down into a small river. keep swimming thru the water until you find a little red cargo box. go up the ladder and as soon as you go into the hole look at the tv screen that the vortigaunt is working. there he is.
3. when the girl talks about the old red barn. and you come to a turn where you can see it. stop. and go up the ladder. grab the ammo and go back down in your boat. use your zoom to see the g-man, standing by a rail. to the entrance into the barn.
4. when you are driving the airboat and you see a couple cargo looking bridges up ahead on top of the (i call it gutter) the g-man will appear standing by another railing at the second cargo box bridge looking thing.
5. when you come to see the first house on the highway level where you meet cubbage and you get the rocket launcher. look up at the top of the house. there he is talking with a man.
6. in nova prospect. on one of the cameras you come to it will show a veiw of a door. it is boarded and just wait staring at the screen and the g-man will appear behing the boarded door of one of the windows.
7. after dog completely destroys a street with an armored car and a few combine soldiers throwing the cars around. when you get put inside the little area with the smashing gate. run to the little gate and jump it. run down the hall and turn to your right to face a little tv. if it is black, then wait for a few seconds, it depends on how early you are there or if you are late and it stays black for at least two minutes then try again. he should occur on the screen.
if you have any questions about the g-man please comment below.