Here is 2 things I want for halo 5.
1 More open campaign areas.
This was promised in interview with Frank o Connor but never came the only true halo game that had huge open maps was the original halo itself. the big open campaigns areas in that game was the highlight so many tactical options and strategies but as of halo 2 you could only go down one path.
2 A in game true skill ranking system.
This is what made halo 2 and 2 so great in the first place not some silly credits system this was what made halo , halo it gave players something to work towards and strive for the works towards and every match you went into you were facing players that was to you're skill if you were good you faced good players if you were bad you faced brain dead players. But if you didn't feel like playing comptive play a social playlist simple easy and effective it suited both types of halo players.
that's all I can think of right now ( or be bothered to type )