Here's my free advice to Activision on how to proceed with Halo:
Step 1: Contact and request an audience with the following original Halo/Bungie devs: Jaime Griesemer, Chris Barrett, Marty O'Donnell, and Marcus Lehto.
The goal of the conversations should be to answer the following questions: "How and why did the 343 Halo games not live up to the Bungie Halo games? How can future Halo games do better in this regard?"
Have those discussions. See if you can find a common understanding. Beyond that, the franchise is Activision's to find success or failure. But perform this necessary due diligence immediately.
Let me use a hypothetical to help make the point:
Let's say that I was given the game director role on the next Half-Life game. And then I was asked, "Hey, would you like to meet and chat with some of the original devs from Half-Life1/2? They would be happy to share their knowledge." My answer would be "Yes, of course. Only a fucking idiot would choose NOT to talk w the original devs."
It would seem that 343/Halo Studios didn't see this as an important part of the process.. and we all know how that ended.
I hope Activision doesn't make the same mistake.