Sadly, I would say the best move would be to simply copy/paste and keep everything the same. The last time the Halo franchise tried to branch out/experiment was with Halo Wars which was excellent, but still did not sell as much as even an expansion pack like Halo 3 ODST.
Just keep everything the same and it will sell just fine. Big first party games like Halo and Gears should only do very minor changes/improvements as fans will reject anything else.








