Alright so I am going to break this down here...
I know a lot of people like the feel of Halo 4 gameplay and everything that comes with it. Then again, there are also people like me who absolutely love the Halo 3 gameplay.
What I think Halo 5 should have is a classics playlist.
Bare with me on this here:
First off, have the matchmaking menu set up like Halo 3 so it is easy to navigate and you have more options for customization throughout and can give that diversity feel.
Second, have the normal playlists like the Halo 4 and Halo Reach style fighting, THEN have a classic playlist. Bringing back Classic slayer, classic snipers, classic team doubles and lone wolves. Have it feel almost exactly like Halo 3. I know for a fact that millions of players would love it. Halo 3 just became available free to download with gold on the marketplace October 16th. Before then, the halo servers had about 5,000 players on it at once. Now that it is free with gold, there is about 17,000 or more people on it at a time!
I also strongly believe that the old ranking system should be brought back into the mix.
You start off as a recruit and you get 1 experience point per match and need to gain true skill levels to get to certain ranks. To me that is the perfect system as it limited boosting with the large servers, and it also allowed players to have two different challenges when trying to get to that beloved General grade 5 rank at 50 true skill and 5,000 experience.
Also, PLEASE PLEASE PLEASE bring back the old custom games styles!!!!
I literally quit playing Halo 4 altogether because I couldn't get all my friends together and play the good ole fat kid that everyone knew, or play a normal game of zombies. I spent hundreds if not thousands of hours playing custom games, mainly infection, when Halo 3 was popular and if that comes back with the new forging abilities, I will spend that much time and then some! And I am sure many will as well!