Halo 5 should have every vehicle from the past Halo games and new vehicles. Same thing with the weapons . Also you should be able to get all the maps from previous games (Halo 2, Halo Reach, Halo 4, ext.) and new maps. It should also have a firefight mode like Halo 3 ODST not Reach, and it should have let you choose if you want to fight covenant or prometheans. Also it should have every game mode from previous games (except for infection, that would be flood). One last thing, it should have all armor from previous games including specializations and spartan ops should be in it along with forge (in forge you should be able to make a elephant, mammoth, short sword, long sword, pelican, and phantom). I almost forgot, it should have all assanations form other games and new ones, same with the armor abitiles, and it should have a custom assanation maker, emblem maker, and a personalize weapon maker (scopes, camo, barrel, and stock).
