I have activated the reactor, I think that is supposed to be the end of the map though, or at least depending on percentage completion of the map, it is the end.

I think that if you get the generators going and manage to flip all of the switches, the center door (that is, the locked one in the middle of the generator rooms) will unlock and allow you to take the elevator to the Alien nest.
In other words, to beat the gamemode in the default setting you need to do this.

1.) Turn on both generators
2.)pull all levers (you can hear each one's alarm)
3.) The door to the infected room should unlock
4.)Pull the lever in the vent in the infested room
5.)I think you can pull the green lever next to the generator
6.) I DONT KNOW