The original big reveal of Halo 2 (which was meant to be long enough that it also contained all of Halo 3) was the Arbiter opening up an ancient Forerunner sarcophagus and seeing a human skeleton inside
I think the reason that Halo fans hated on Halo 4's story is because they couldn't handle anything with more depth than a shallow pond.
"WhAt aBouT HaLO Two!?" They hated that back then too lol (and that's why every character from Halo 2 lost 85% of their braincells in Halo 3)