I love the day night cycle , but it think Bungee missed a trick with the night time.
Imagine the sense of foreboding as you see the sun setting, knowing that the higher level Hive masters are going to be out in numbers, and that the darkness will cover the land making visibility limited without your ghost light.
Will you survive the night or succumb to the darkness....
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Also I think the fallen should be a bit more stealth like in the dark. Your ghost mentions, that the fallen thrive in the dark so make them as if they appear out of no where, or make them a bit more... Smart so to speak. since in the dark they are more capable enemies, they should be more deadly as well.