Not sure I'd compare it to Halo but hard to explain without spoilers. No idea about Forerunners and the flood.
I was just going by the paragraph description about humans expanding throughout the galaxy, and stumbling upon something "bad" (or, assumed bad, by the description given).
And my 15 year old recollection of Halo 1 and 2, Humans uncovered the Flood (alien race) unintentionally releasing them to rampage across the universe again. Flood = Zerg, basically. Starcraft, Halo, all share similar elements. Though some details may be different, the idea that Humanity mistakenly uncovers or comes into contact with something that others who had been there before us would have preferred stayed hidden or left alone.
Can't sleep, clown will eat me.