We've seen this set of rumors, supposedly coming from someone whose uncle works at Bungie (oh dear God not again--Ed.) several times in the past few days. They were even translated into French at Halo.fr.
Given that Bungie seems to be enduring some kind of self-imposed silence bordering on self-denial with regards to the very existence of Halo 3, even to the point of failing to confirm or deny the existence of the game after it was referred to by no less a personage than Microsoft chairman Bill Gates.
That, plus the fact that historically Bungie, like other game studios, usually doesn't comment on rumors, means that regardless of the particular situation right now, these rumors would no doubt spread unchecked anyway.
However, in the interest in helping promote a slightly less credulous Halo fanbase, I thought I'd provide a few comments on each of the rumored items.
So here we go:
1) It will have a darker and more gritty story than the previous games.
This is so vague I hardly know how to respond. In Halo 1, you are (supposedly) the final SPARTAN escaping in an old spacecraft chased by a Covenant armada and crashland on a strange ring, which turns out to be a weapon of unimaginable power and a prison for an unimaginable terror, the Flood, which poses a dire threat not only to you but the entire galaxy. Your marine cohorts are decimated and you're forced to detonate the engines of your ship, killing the Covenant and the Flood and destroying the ancient artifact. To the best of your knowledge, when the game ends, you and Cortana are the sole survivors.
It makes me wonder what qualifies as "darker and more gritty."
True or False: Not applicable. You can't evaluate such a vague claim. All you can do is ignore it.
2) They're attempting to maintain an online cooperative component for the campaign supporting more than two players at once.
They also might be attempting to wrap a lemon around a large gold brick. But let's not overdo it. Online coop didn't manage to make it into Halo 2, so I suppose it might make the cut in the next installment. However, the last two games have also been under tremendous pressure to get done on time, and the rumored schedule for the release of the next game is even tighter. Assuming it's true.
True or False: I'm going to say false. I'd love it if this made it in, but it seems to me far too much of a leap to go from no online coop at all to coop with more than two players. It sounds like this is being made up.
3) It has a lot of cinematics planned for it. The opening scenes apparently occur thousands of years before the timeline of the original Halo: Combat Evolved's story.
Saying a Halo game has "a lot of cinematics planned" is like saying the ocean is wet. It's a pretty easy prediction to make. That one or more such cutscenes might cover a much earlier part of the story is also quite plausible.
True or False: True, but probably unimportant. Of course the game will have cutscenes. The bit about cutscenes from thousands of years in the past sound like the deleted part of the Mural cutscene; I tend to doubt Bungie is going to reveal anything shocking like the identity or whereabouts of the Forerunner or something similar in a cutscene.
4) It will have a multiplayer mode which pits players against bots in scenarios that are directly connected to the story of the game.
Pure wishful thinking. If it wasn't already obvious, this one alone removes nearly all credibility the source has. Bungie hasn't ever done a shooter with bots, and it was explained while Halo 1 was still in development why the artificial intelligence they made for the game was better suited to in-campaign enemies and allies than bot-style multiplayer. If it didn't make it into Halo 1 or 2, it seems doubtful Bungie would commit the time and resources to adding this feature for the third installment.
UPDATE: As pointed out by a comment below, Marathon did has bots, so it would be more appropriate to say Bungie hasn't done a modern shooter with bots, or hasn't ever done a shooter with modern (post-Steven Polge bots). In any case, I stand below the prediction below: no bots in Halo 3.
True or False: False. Bungie's got an epic story to continue and new hardware to write for. While Halo 3 may end up having some new features, I think it will be more about incremental improvements and polish.
5) They're attempting to implement both a map editor and a movie maker, which would allow players to send and receive their maps/movies through Xbox Live. This would apparently be on a separate disc, and they have an entire team working just on these two projects.
This sounds much too ambitious. While it appears as if Halo 2 did, at one point, have a movie recording feature that was disabled or removed prior to shipping, the idea of an in-engine map builder like Pariah seems highly unlikely. It would be a huge undertaking to add this feature. It may be understandable why Microsoft might want this feature in the game; reviews of Pariah gave kudos to the map-building feature, with the downside being that once you made the maps, you can only play Pariah on them.
However, taken along with the other ambitious predictions, this one just looks gratuitous.
True or False: False.
6) Zanzibar, Sidewinder and Hang Em High are said to return to the multiplayer mode, completely reworked. Zanzibar will be mangled and torn apart as though after the battle, the sky will be dark red. Sidewinder will have four legs instead of just two, with bases at each end. Hang Em High will have a massive tree at its center and the structure will be deteriorated.
This again is more likely wishful thinking. Hang 'em High and Sidewinder were two of the most oft-requested maps to be ported from Halo 1 to Halo 2. Bungie instead chose to bring Blood Gulch and Beaver Creek, and then later Wizard, because they felt those maps were better suited to the new game.
While this could be true and might even happen, it seems like some specific details made up to give the other predictions more believability.
True or False: False.
7) They want to support more than fifty players on Xbox Live for certain maps.
Now the real source of the rumor is revealed; the game in question is actually Perfect Dark Zero and not Halo 3 after all, as fifty-plus player support was just announced for the title earlier this week.
True or False: False. This would require not only a major revamp of the networking engine, but also vastly larger maps and completely different gametypes.