- last post: 01.01.0001 12:00 AM PDT
The party line as adopted by Bungie in the Halo 3 FAQ in the main site is fairly telling:
Q
Is this the last ever Halo game?
A
It is the conclusion to this story arc.
That is to say, Halo 3 will be concluding the individual tale of the Master Chief squaring off against the Covenant in an effort to prevent the galaxy from being vanquished by the Halo stations once more, as has been the general scenario of the previous two games. However, it does not preclude further, separate adventures being set in the Halo universe.
For instance, to throw out a few random concepts, we could have a game set out in the distant past where the Prophets first discover the holy scriptures left by the Forerunners and begin the glorious crusade of the First Age of Reclaimation, with lots of satisfying battles and millenarian fervour along the way. Alternatively, we could have a tale describing someone's attempt to survive the disastrous first contact between Man and Covenant. Or another idea is how 343 Guilty Spark becomes bored with sweeping up dust in the Alpha Halo control room for centuries on end and so begins an epic seven-game saga where he utilises a secret time machine to subtly alter history across the entire galaxy so that it happens to rain marshmellows and broccoli over Leeds in 2148, encountering lots of hi-jinks, scrapes and capers with Fred Flinstone, Sir Harry Flashman, a baby Prophet of Truth and the God-Emperor of All Grunts from a parrallel universe along the way.
As you can see, they'd all Halo games, just pursuing different plots to that of the present series.
[Edited on 5/18/2006]