2007 was around the time Microsoft (and as such, their flagship) took a turn for the worst. Backwards Compatibility development halted, mappacks stopped becoming free and instead became mandatory, expansion packs became standalone games with price markups, and the general focus shifted from core gaming to casual consumption.Screwed over non-US players during the H4 launch period and constantly lied with a straight face. We still don't have multiplayer filters, something Bungie gave us in 2007.
All in all it feels like a studio that doesn't enjoy what they're doing.
In the midst of all this, Bungie exchanged their Magnum Opus for independence.
If you're a true Halo fan, you've got to let it go...