There is something I really don’t understand about the campaign.
We have seen at E3 that the Infinity enters Requiem and crash-lands somewhere in the jungles, making its descent over the Master Chief. When the Chief goes after the starship, he first encounters the Prometheans. That’s the mission INFINITY.
Now we have seen footage from the Mission FORERUNNER which takes place BEFORE INFINITY. It’s this dark level where the Master Chief heads to a relay. In that level, Covenant AND PROMETHEANS fight the Master Chief. It is also the level when the Chief enters the Chamber of the Cryptum. And there is a broadcast from the UNSC Infinity which is still outside Requiem’s shell, approaching it in search for the wreckage of the Forward Unto Dawn.
So something about the E3 Gameplay must be wrong because obviously the Chief encounters the Forerunner forces before he arrives at the jungle area. Maybe the E3 Campaign Gameplay was wrong or remade or so?