First To start, Adrian shepard from Opposing force may be in ep3. Due to the fact that at the end of portal, his name is Highlighted on the keyboard. Barney from blueshift has already appeared in Hl2. And Gordon Freeman, Is Most Likely Gman, For the following reasons.
- In His Locker in hl1, he has a Blue suit like Gman’s
2.G(ordon free)man - Gman Has a sort of way of popping up wherever gordon is, Like Monotoring him, maybe attempting to keep his past self from Screwing up.
- In Kleiner’s Lab when he opens the back door, The Photo that he moves to open it, is a Photo of black mesa’s Scientists. One of them looks like Gman, And Gordon Combined.
Also, Maybe in hl3 you will go Back to Black Mesa. Why i think this?, In Kleiners Lab there was a HEV Plate., if you look around you’ll see it.
In Conclusion, these are all reasons that i think what i think.