!!!WARNING!!!
This article includes spoilers of the game Half-Life 2. If you have not finished it then I recommend you finish it before reading.
I've been playing Half-Life 2 a lot and I just wanted to show a few screenshots of the G-man sightings.

This is his first sighting, The beginning of the game. Chapter 1 “Point Insertion” He tells you that your time has come again. You appear in a train entering City 17, starting your new adventure. One of the citizens on the train say that he did not see you get on the train.

This is in Chapter 2 “A Red Letter Day”. You meet Dr. Isaac Kleiner,
Your main MIT teacher. He also worked at Black Mesa. He has also modified your HEV Suit from Mark 4 to Mark 5. The main modification were Neurotoxin healing, Zoom view, Sprint and an AUX Power indicator.

After Dr. Kleiner's teleport incident, you strangely appeared in Dr. Wallace Breen's office. He recognized you eventually and started the whole Combine Metro police to hunt you down. You are now traveling the old canals to Dr. Eli Vance's hideout. It is tough dodging Civil Protection for Gordon, but he can handle himself out there.

One of the Rebels have given you an airboat. You must get to Eli Vance's hideout before the Civil Protection spots you and sends a hunter-chopper after you.

Yes, eventually I had to cut off the fifth one. The screen was blinking hardly and I just couldn't get a good shot. Anyway, your stealthy plan didn't work and a chopper is going after you. But thanks to a few rebels and a vortigaunt, you got a turret mounted on your airboat so you can defeat the chopper and any hard defenses by the Combine.

Note: I do not use cheats for the game. I play fairly and I only use cheats for occasional times (like this one). Shortly after you get out of Ravenholm. You get to have the Over watch Standard Pulse Rifle or AR2 for short (The gun I am holding in the picture). About the gun: It was designed to fire small bullets that are combined with dark matter. And dark matter is a kind of special energy that when a mere cell or molecule touches it, it gets wiped out. You will use bigger dark matter balls in the two chapters “Our Benefactor” & “Dark Energy”.

Not many people can find this sighting. The thing about G-Man and Odessa talking is that G-Man wants Odessa to give you the RPG Rocket Launcher. But I'm suspicious that G-Man gave Odessa your old Rocket Launcher from Half-Life 1, but he has modified it (At the end of Half-Life 1 G-Man takes all your weapons)

After breaching into Nova Prospekt (It is called Prospekt with a K for no reason) you need to rescue Eli Vance. The new Combine Prison Guards are a bit tougher then ordinary Combine Soldiers. Also at the end of Chapter 9a “Entanglement” When your teleporting with Alyx, You can see a few new Combine Soldiers. They are in a white costume and have one red eye. These are called Combines Elites. They are the last type of Combine you'll see (Or maybe not?).

The tenth sighting was even harder to get, then the fifth one. Since it only appears once, half a second and explodes. You are back in City 17 and are ready to cause some more terror and chaos to the Combine. You are heading for the Citadel. You've got to meet up with Barney.

You destroyed Breen and his teleport… Eventually it was also the dark fusion reactor. And that explosion means “Bye bye, Citadel”
The rest is continued in Half-Life 2: Episode One.
Copyrighted by Freeman 2008-[INSERT INFINITY SYMBOL HERE]