Things you might have missed from #1
It seems like Theed (the man who leads the "blue" team) has some kind of psychic connection with Maculox. He is able to see the result of Marylin's activation before opening the door.
The plan for the wraparound cover detailed at the back of the book actually reveals quite a lot. Each of the characters is indicated by their real names, not their codenames. The "leaders" of the red side are revealed to be Janus and Anita. Two characters are labelled as "New Girl", indicating that each side will recruit a new female member.
The floating monster is Kaspar, aka "Phantasam", and his ability is teleportation of others (and presumably himself).
Halle, aka "Thrasher", the baboon-like monster on the blue team is female. Based on the design alone, this was a surprise to me.
The one giving orders on the red team appears to be "Siren". She is the only one other than "Imp" who speaks during the Black Mesa raid, and it's to give orders.
"Imp" may have originally been recruited for his computer hacking ability, as he claims during the Black Mesa raid. This suggests that the members of the teams may be chosen by utility.
When Marylin meets the amateur hacker, he shows her an image taken in Pripyat, Ukraine, which shows a member of the "blue" team who is not shown anywhere else. This may be a member of the team who has already died in the month between the Pripyat incident and present.
Any other details you noticed that I didn't? Add them in the comments. Keep it to #1 though!