So I'm in the camp that thinks Halo is overrated and mediocre, and I came to that conclusion after playing a ton of it with a buddy. However since I got a launch slim console, I dcided to give the Halo phenomenon another chance and picked up Halo 3. I don't know much about the story beyond the basics. I know Halos are planets. There are lots and lots of them. They are meant to detroy all sentient species. They were created by the flood? Covenant thinks flood is gods? So thats basically all I know. Anyone care to explain the basics of what happens and maybe some of the emotional ques I should pick up on. Perhaps whats up with Cortana, and how did Halo 2 end exactly.
 
I tried wikipedia, and it's a bit too complicated for me, so I need it presented simply. Bullet points maybe?

Basically the Halos were created by an ancient race which were supposedly destroyed by the flood which the covenant revere as gods and are trying to turn on the rings to destroy all sentient life in order to destroy the flood because the flood need other life forms to survive. In the first Halo Masterchief destroyed a Halo but there turned out to be more of them and in Halo 2   he stopped another ring from going off but he didn't destroy it and all of the rings started up again. During this whole thing the covenant found earth and are trying to invade it. Also there has been a rift in the covenant and the Elites who have been the main antagonists are now out of the covenant and the brutes have become the leading faction within the covenant. So now the elites and humans are working together. Masterchief is now aboard a covenant ship on route to earth. Cortana (his AI companion) has been left on one of the rings with Gravemind (the collective consciousness of the flood) and he is trying to retrieve her while saving earth and stopping the covenant from activating all the rings at once and destroying all life but he also has to find another way to destroy the flood since they are also a huge threat.  
 
That's what I remember from the games anyway. There is more details but really that's the main stuff. I'm sure someone else could explain better but that's my understanding. Feel free to ask me any questions and I'll try to answer them. I really like the Halo games and think they're great but I have a friend who just doesn't like them and we've tried to play multiple times and he just doesn't like it so I know for some people it's just not their thing. 

There's some aliens. And their bad. And then Bungie forgot to turn up the gain on the dialogue tracks in Pro Tools and no one could ever fucking hear anything anyone said.
 
The End.

" @valrog:  I'd rather not. I don't want to dig through many pages to try and get an understanding of the story that can be succinctly explained to me by a user.
 
@triple07: So what exactly happened at the end of Halo 2? Did Chief leave Cortana and then plummet down to earth? Also is Arbiter an Elite that you mentioned? Why did the Elites turn on the rest of the Covenant? "

"@triple07: So what exactly happened at the end of Halo 2? Did Chief leave Cortana and then plummet down to earth? Also is Arbiter an Elite that you mentioned? Why did the Elites turn on the rest of the Covenant? "

" There's some aliens. And their bad. And then Bungie forgot to turn up the gain on the dialogue tracks in Pro Tools and no one could ever fucking hear anything anyone said.  The End. "

There are bad things, and good guys go and murder them.
 
This same summary can be applied to most action games where you're unsure of the 'story'

I tried wikipedia, and it's a bit too complicated for me, so I need it presented simply. Bullet points maybe? "

Forerunners make a bunch of cool stuff, run into the Flood, who nearly wipe them out.  Forerunners build Halos to wipe out all life, leaving the flood with nothing to infect, but the Forerunners also keep some species preserved so that the universe can be repopulated.

Covenant revere the Forerunners as Gods and think that they ascended to a higher plane of existence using the Halos.  Humans are recognized by ancient Forerunner tech and AI as 'reclaimers', and the Prophets proceed to flip the fuck out and declare genocide towards humanity, because if news gets out that humans are related in any manner to the forerunners their alliance would fall apart.

Master Chief accidentally landed on a Halo, woke up the Flood, and destroyed the Halo during his escape.  The Covenant see this as the equivalent of drunkenly breaking into the Sistine Chapel and painting dicks all over the ceiling before you leave, and the highest ranked Elite that Master Chief didn't put a bullet in during Halo 1 is branded a heretic for failing to protect the Halo.  He's declared the Arbiter and proceeds to be sent on suicide missions left and right,

During one such mission, the Arbiter discovers that the Humans are seen as the true inheritors of the Forerunner technology, and that the Prophets have betrayed the rest of the covenant by hiding this fact from them.  The Brutes, being large, stupid, and easily controlled, are ordered to destroy the Elites to keep the secret- The Arbiter kicks ass, takes names, and splits the Covenant Armies to side with the Humans.

During all of this the Flood is basically rampaging around like a bunch of assholes, and infecting people left and right.  The Covenant find Earth by accident, Master Chief fights them for a while before being captured by the Flood Central Intelligence, the Gravemind.  The Arbiter also gets himself captured, and they agree to help the Gravemind destroy the covenant because he's big and they're stupid.  Big surprise, he betrays them later.

Ah Covenant, and the Covenants over there. Holla if you get the reference.

" @august:@EvilTwin: This may be a dumb question but is Master Chief the last Spartan? As in, did they rest die on Reach? Also I heard something about there being different Spartans. Something like Spartan 2 or something like that? Is that right and if so, what are the differences besides regenerating health. "

" @august:@EvilTwin: This may be a dumb question but is Master Chief the last Spartan? As in, did they rest die on Reach? Also I heard something about there being different Spartans. Something like Spartan 2 or something like that? Is that right and if so, what are the differences besides regenerating health. "

Man, the names of everything in Halo are so heavy handed. 

Halo stole from Stacraft, Stacraft stole from Warhammer 40k. You don't need to know anything else...

Important to semi-important characters, as a supplement to Make_Me_Mad's post:  
 

• Master Chief (John-117) -- Ostensibly, the last living Spartan supersoldier. Operates within a high-tech MJOLNIR body suit that gives him regenerative energy shields along with a number of physical augmentations. The Covenant begin referring to him as "The Demon" after he single-handedly destroys a Halo. 

• Cortana -- Female AI who rides shotgun inside the Master Chief's armor. She is modeled after his creator and often acts as the sassy, hyper-intellectual foil to his stoic, militaristic personality. At the end of Halo 2, she is left on the Covenant military world so that the Chief can more effectively chase down the Prophet of Truth.

• The Arbiter -- Covenant Elite general charged with heresy after the destruction of Halo. Instead of being executed, he is made a special operative tasked with suicide missions. He learns during Halo 2 of the true nature of the Halos, and, feeling a deep spiritual despair, rallies the Covenant Elites against the Prophets and Brutes at the end of Halo 2 and during Halo 3. Should be considered the Master Chief's militaristic equal. 

• Captain Jacob Keyes -- He is the captain of the ship Master Chief's on in Halo 1. Super highly-esteemed naval officer and tactician. He's absorbed by the Flood and euthanized by the Master Chief at the end of Halo 1.

• Sergeant Avery Johnson -- Token black dude. Sam Jackson in military fatigues. He's got a cigar in his mouth and he can talk some trash. He somehow survived the events of the first Halo (explained in the novels, not in the games), and became somewhat important to the story in Halo 2. He's pretty good with a gun. 

• Commander Miranda Keyes -- Jacob Keyes's daughter. Introduced in Halo 2. She's basically assigned to assist the Chief in any way possible, after the Covenant invasion of Earth in the beginning of Halo 2. 

• The Covenant Prophet of Truth -- The Covenant's religious leader. Power-hungry, megalomaniacal. Orchestrated the deaths of the other religious figureheads so that he may control the entirety of the Covenant. Believes that firing the Halos will grant him some level of godly power, perhaps ascending him to the level of a Forerunner. Seems oblivious to the notion that Halo will kill everything. 

• Gravemind -- The Flood hive-mind/aggregate leader. Seems near-omniscient and has total control over the entirety of the Flood on a telepathic level. It's in its best interest to prevent the Halos from firing (obviously), and its chief desire to consume every last sentient being in the galaxy. Looks like a giant venus flytrap. Or maybe the thing from Little Shop of Horrors. Speaks in trochaic heptameter, which doesn't mean anything except good-luck-understanding-anything-of-what-he-says. At the end of Halo 2, he uses the Flood to commandeer the Covenant War-Planet, High Charity. 

• 343 Guilty Spark -- A Forerunner "monitor" AI installed in the first game's Halo to keep watch over the Flood being contained there. Directly manipulates the Sentinels, who collectively make up a Forerunner security system built to deal with small-scale Flood incursions. Very good likelihood that 343 Guilty Spark is insane with time, since the Forerunners have been extinct for several hundred thousand years. Sergeant Johnson affectionately refers to him as "the light bulb."