Halo 5: Guardians has been announced by Microsoft today with a release date of Autumn 2015, exclusive for the Xbox One. It is unclear at this point whether or not Halo 5 will be split into multiple games, as was the case with 2009's Halo 3: ODST.
This wording suggests that 343 are building Halo 5: Guardians around the franchise's community, suggesting further that the game might include largely online play. As well as perhaps gearing towards a more online-based experience, many hints have been given that this game will be all about the "journey", but what type is currently unknown.
Overall, a cryptic first announcement, but then again, what game reveals aren't these days?
More information is to be expected to be released at E3 2014 in June. Stay tuned!