Black Mesa: We've Got Hostiles!

This is Chapter 4 of the Black Mesa Incident...
''System: reboot completed.''
Okay... Another great day... But not so great. I am now on another place. There's a scientist over there yelling at a guard and he was like a insane psycho that is banging a window.
"OH MY GOD! OPEN THE SILO DOOR!"
The guard got caught by a zombie, got drag into the vents. And then he got killed. The scientist was getting so INSANE and he was out of his mind. He ran towards a laser-camera but as he pass through it, the scientist died because the camera exploded. And I was like...
"Oh god! I got to get one of those things so I could trick someone."
There's more ammo and I saw a scientist running to a Marine. I though I am now safe. What a fool again! That Marine killed him and so he shoot me. I thought he was out of his mind and when I killed him, I grab his M4A1 and still got 3 more rounds. There's a lift next to the dead scientist where I use it and it leads to the surface.
"WOOHOO"
As soon as I got out from the big hangar, the surface is there, the bright sunlight. And the asphalt road. Little I know, the other Marines kept shooting me and I am still trying to think that they are all crazy but I know the reason they want to kill me. Because I am the primary target.
A few minutes outside. I was forced to crawl into a hole leading underground and I was no hope for escape when they are bombing and sending more troops. I got further down to Black Mesa and grab some few ammo's and then,there's this thing called barnacle that catches someone or something that touches it's tongue. More Soldiers came and their patches says: HECU Marines.
They has came to kill me and after a few mazes, I manage to crawl to a vent that leads to the Silo Door control room where the guard is killed. Another scientist is over there that came before me. He said:
"Gordon, I am hiding here and watch out for those Soldiers! They are sent to silenced the remaining personnel alive including those who are part of the experiment. Specially you. But be careful Freeman! Don't get killed."
I click the button that opens the Silo Door. And now, I'm gonna face a big yet dangerous thing that is very aggressive and sensitive.