I don't think 85 is a very good score for a long running exclusive flagship title to have. A lot of reviewers will go easy on the game, just because it is a big name franchise. A flagship exclusive is supposed to be pulling out all the stops, and making the very best game you can possibly make. Your biggest best effort doesn't break 90?
If Halo was a brand new franchise from a medium sized developer, then 85 would be an amazing score. If I had an XB1 I would get this game for sure, but I'm not buying a system for it.