here are some stuff that I always wanted in halo and never made it in reach.
-Multiplayer Bots (With working medals etc.)
-Better Forge (With terrain and texture editor especially)
-No brutes (This is not planet of the apes)
-Simply more weapons not new weapons instead of old ones (if your worried that it could be hard to balance in matchmaking, just allow them for custom games, you know we like custom games)
-The BR
-No bloom
-More than 16 players multiplayer (32, 64, etc.)
-Full time ragdoll death animations, just all the time
-Violence (the game is already mature guys, cmon, a sword lunge should slice someone in half, rocket should do more damage, more blood)
-Permanent armor damage until you respawn (the more you get hit when your shield is down, more your armor will become damaged and it will look damaged, if you get headshot by a sniper, it probably wouldnt explode the head but you should see the hole in his helm)
-Forced first person vehicule control (its just more realism IMO)
-handicap
ill edit when I think of more stuff