Cant really be arsed to put spoiler tags inso if you dont want to see some theories, look away now (though in my mind you shouldnt be in this thread if that is true). Hopefully there arent too many spelling mistakes on my part.
There are a few things I can't really get my mind around though - have the forerunners ever fired the Halo rings to starve the flood and exterminate themselves in the process?
If you pay attention to Guilty Spark when you confront Tartarus (I would be amazed if you played the game and you missed it), he says the Forerunners as a last resort fired the Halos, bringing their "presumed" destruction.
But then, how did the Flood survive?
The Halos kill off the Floods food, all sentient life as explained by Guilty Spark and Cortana in Halo, not the flood themselves. As to why there are still alive? They may just simply live a very long life which is I guess one reason why they were considered such a threat in addition to their parasitic nature, or perhaps beings from other galaxies once in a while find the Halos and are consumed, prolonging the the Floods existence.
Anyway, like I said, I think Forerunners fired Halo, took themselves out, sent the Ark to earth.. Humanity evolved, took to space, met covenant, found halo.
Probably very likely in the general scheme of things. The Ark of course has the connotations to Noahs Ark, maybe it is somehow immune to the Halos pulse thingies allowing some survivors to relocate and begin society anew in addition to setting the Halos off.
YET, this does not even begin to explain how the covenant religion is so deeply embedded with forerunner symbolism like "Halo" and "The Great Journey" (reminds me of the Ark..) Maybe the flood did not use a single ark but several aimed at all habitable worlds they knew, and the covenant species and humans are both descendents of the forerunners. Don't ask me why only humans can use Halo, though..
Perhaps the Prophets interpreted the Forerunners as so great a being, gods even, that they simply wish to follow in their footsteps, destroying themselves and starting their journey to where ever they believe the Forerunners went in the process.
Either something like that or they are extremely stupid and naive, but Truth comes across as being a sly bastard and considering they had Guilty Spark I would be amazed for them to have so badly interprete what he was saying, especially since he has no trouble telling the Covenant that their verbiage is wrong.
As for Humans being needed? It would tie into the Ark theory in that they are Forerunner descendents, which explains why Guilty Spark and Penitent Tangent (which is a great name, showing perhaps that the forerunners showed much regret and remorse over the halos) view you as the reclaimer, and maybe why Gravemind says something along the lines of " we came here as enemies but will leave as brothers", either he knows that humans have faced the flood before somehow or he sees you as a Forerunner (which I admit is a long shot) or that he was just referring to the Human/ Covenant conflict or none of them at all
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The Forerunner ship is the Ark, not Earth.
The Prophets' faith seems to be built on scraps of lore found in Forerunner ruins, interpreted in a religious context. My theory is that they uncovered contingency plans for use if the Flood ever became impossible to contain--'in such an event, the rings must be fired to sterilize the galaxy. Selected individuals will report to this transport vessel before sterilization commences. They will proceed to the world at coordinates (xxx,yyy,zzz) and repopulate it, then use it as a staging point to reclaim the remainder of the galaxy,' or something to that effect. As interpreted by the Prophets, this emergency procedure (which may have been discovered aboard the Ark itself--apparently they've had that Forerunner vessel for a long time, long enough to make it an integral part of High Charity) became an article of faith, a prophecy of a day when the impure would be destroyed and the chosen races would embark on a Great Journey to a promised land, where they'd be granted dominion over the entire galaxy. Of course, what these guys don't realize is that their 'prophecy' already happened.
Then why did they go to Earth...twice?
Personally my view is helped by the books that suggest that artifacts have star charts on them leading to forerunner installions, homeworlds etc. Regret headed to Earth perhaps knowing it to be hugely significant as the Ark or not, went to New Mombassa after finding the planet to be populated to quickly get a artifact which then led him to Delta Halo as they didnt know where it was previously as Truth was well chuffed that "another sacred ring has been found!" (either that or hes lying to the Arbiter).
The Covenant learn of the Ark or just its confirmed location from Guilty Spark leading them back to Earth. Why go back to earth in the Forerunner ship? Perhaps just for their religious significance, it would surely be seen as a huge event by the Covenant. Maybe they need a huge power source to fire the Ark and duracell batteries just arent good enough?
Maybe the forerunner ship is the ark, and Earth is outside the Halos blast range and desinated a safe place to use the ark (dont belive this for a moment myself). Maybe Truth just didnt want it left in the over run High Charity where the flood could steal it, though this would imply he has decided that High Charity is a lost cause since the ship was meant to power it.
IGN said:
For those with issues, the Arbiter was not as cool as Master Chief. Bungie introduced the Arbiter as a second playable character and throughout the game, and it forced players to switch back and forth between the two. If you were willing to accept playing as the Arbiter, then the experience brought with it an interesting story, and a few neat hooks. But to leave the game as the Arbiter, not as Master Chief, was disappointing. There are very few characters as cool, macho or as generally bad-ass as Master Chief in the history of videogames. And for a character who doesn't say much in the game, that's saying something.
Perhaps it was just me, but I never really thought of MC as cool in Halo (or its sequel) and his voice came across as very forced trying to emphasise this in Halo 2, kind of like how David Hayter hasnt really been able to top his original voice acting in the MGS series. Either way I really liked the Arbiter, he seems alot more fleshed out as a character and I really felt for him when he realised he was getting screwed by Tartarus and the Prophets.
As for the ending, I thought it was a horrible way to end things, I felt the story just stopped not even bothering to bring some closure like Halo did imo but it will atleast provide a nice platform for the start of Halo3 which I guess Bngie wanted.
But please get back to me and tell me what you think. I think the facts speak for themselves. God, what a great twist! But it's hard to grasp for some people. My little brother didn't understand either. But it makes sense 
