Second time playing through the game, first time was for fun beat the game in like 4hours on 4 player co-op.
This time I got the Long Wolf Achievement, so I actually watched the cutscenes and such from start to finish.
So…
From my poor memory:
The Forerunners rebelled against the Prescursors, and then the Forerunners took over the Galaxy, and watched over and protected the evolution of life between species. They believed in peace so they gave up their weapons. Then the flood came, and started eating everything, so the Forerunners decided to Nuke the Galaxy with the Halo Rings and preserve life through data samples, robots, and embryos that were redistributed which recreated all the life once again on the living planets.
The “Didact” was a Forerunner who was against building the Halo Rings, and thought it was a “sin”. He believed instead everyone should just be converted into cyborgs. Prometheans. Well he was left on some flood infested planet, and locked away or something.
So Halo 4, he wakes up, finds his weapon, and tries to destroy/turn humanity into cyborgs.
Meanwhile, the only person who knows about this seems to be Cortana, and Master Chief, and Cortana is degrading while on her period.
Also, for some unknown reason the Aliens are against you, and want the Didact to do it’s thing, even though I thought humans and the covenent made peace in Halo 3…
oh well…so basically no one knows what Master Chief is doing, and he meets the Librarian (Wife of Didact), so apparently some forerunners were kept alive. She gives you unknown powers, and it seems “evolve” master chief into something that can’t be converted into a Promethean.
->>> Skipping to the end. Didact gets his weapon/spaceship, and fires it at Earth destroying a large city. At the same time MC is like “I got a nuke” and the Didact tries to stop him, but then Cortana goes all crazy mode, and MC goes all crazy mode, and the Didact falls off onto Earth, and the MC goes suicidal blows himself up, but Cortana “mysteriously” shields him and touches his chest, cuz she loves him so much.
Then…Master Chief is like i don’t care, do what i gotta do, and the Commander is like humans and machines are different, and MC is all like “hmm that’s what Cortana said”, and then Master Chief gets his armor taken off, and removed his helmet, and you see his eyes. The end.
So since everyone keeps calling him a machine, he was genetically enhanced, and the Librarian said he’s one of the special seeds, perhaps Masterchief is somehow a Forerunner who had more of his “powers” unlocked with the Librarians genetic gift of whatever.
and I don’t understand the whole love story between Master Chief, and his robot girl. Guess that’s just a guys fantasy. To have a hot chick inside you all the time. But eh, Master Chief didn’t really care that she died, he’s just like “Let’s do this” Boom Boom Rocket.
Conclusion:
This entire genre is very similar to Dragon Ball Z
Goku = Master Chief
Goku as a baby sent to “Earth” raised as a human, while “almost” his entire race and many others were wiped out by Frieza/Flood.
Than the few saiyans that remain come back and tell him he’s a super saiyan, and there’s only a few super saiyans.
^ Basically what the Librarian told Master Chief.
Also, since Master Chief never takes his gear off, never goes to the bathroom, doesn’t care about much, does not age, and is Godlike, it would appear that he is some Forerunner who began as a Manipular, and perhaps the Librarian evolved him to the first form.
Besides the point, Halo 5 will be on Earth, most likely fighting Prometheans and the Didact again, and hopefully the flood will return, so it’ll be like robots vs Zombies vs Master Chief. 
