Actually really agree with the bolded. Then I wrote a long post not many will read...
I honestly think they should have straight up copied Call of Duty in one aspect (and one aspect only). COD makes minor graphical updates and changes very little in the way of core gameplay year to year. They basically make small iterative changes to a game everyone has know, essentially, since MW2 hit the market. On top of that they release a game every single year. In a yearly development/release cycle two things become de facto. 1) You don't have a long time to implement massive changes. 2) All of the smaller changes are more readily accepted by your fanbase because they are all used to your pace and the rate at which the game has progressed to date.
In Halo, with a 3 (or more) year development cycle those two things that have made COD so successful are now working against you. With a longer development time you now have the potential to throw a lot of changes into your title. At the same time the core of your fanbase, the kids/pros/adults/etc., that are still playing your game a full three years after launch have now grown accustomed to a specific iteration of Halo. When you introduce a new game mechanic (especially some of the changes that are so obviously borrowing from other titles) it becomes jarring, abrupt, and shreds a small (or large) part of your most die hard fans. This becomes a downward spiral as you continue to chase larger and larger sales (with larger budgets, more bells and whistles, and more new features copped from other titles) while consistently leaving your core fanatics farther and farther from the Halo they want.