[quote]more than 4 enemy factions in one level[/quote] Uhh. Halo: CE is the pinnacle for this so far, and it has a maximum of four if you include John as a member of the UNSC. Sentinels are Forerunner. Perhaps you could have some controlled by the Iso-Didact and the remains of the Librarian, some by the Ur-Didact, accompanied by Prometheans and/or actual fighting Forerunners (presumably, given their size and power, they'd be at least Hunter-tier). The Flood would already be one of those factions. So I guess it could be managed with UNSC vs. Storm Covenant vs. Flood vs. Didact vs. Librarian. And, if you believe the Precursors are going to make an appearance in the game, chuck them in too, although my bet is that their return happens at the end of H5.

I just want to see Sentinels have an actual role. There are both enemy and friendly Sentinels on Midnight but they do not interact with anything (except in the easter egg). Only in Requiem and Reclaimer do AI even notice them. Even then, they do not have combative AI outside of scripted parts (Sentinels vs. Hunters). I've glitched the Sentinels on the aforementioned levels so the Covies and Prometheans actually shoot at them but they do not shoot back. The only time I was excited about them was in that Spartan Ops chapter featuring Sentinels vs. Watchers. Hopefully.

What Easter egg?

The 3 Battle Rifles on Midnight