I have alternated some of my ideas: (please note I think one of them was not my idea, but a fellow member's. I will point it out when I bring it up.)
Ok so first, with forge, there should be forgeable: drop pods, pelicans, phantoms, vultures, wolverines, locusts, elephants, hornets, falcons, (yes hornets and falcons), navy boats and aircraft carriers, and space banshees. What should MAYBE be forgeable: scarabs, corvettes, UNSC frigates, sabers, cobras, Seraphs, and unlikely, super carriers.
There should be a much bigger forge budget, maybe 35-50000$, much larger item quantities.
Forgeable working doors, changeable weather conditions, bigger forging area, multiple forging worlds, the option for no teams, an option for destructible environments, and simpler way to make a map valid for a certain game type.
Ok, now multiplayer. Here it goes:
Updated playlists; bigger teams on big team battle, like 20 Vs. 20, and here is where my buddy's idea comes in; he basically said there should be two frigates: one human, one covenant. (corvette). Everyone would spawn in their frigate, and can choose whether they want to pilot the frigate, get in a saber or space banshee/seraph, or get in a vehicle to protect the frigate from indoor attacks. The frigate can only take a certain amount of damage, then it gets destroyed. After a team's frigate is destroyed, tgey have to survive as long as they can without dying, because, well, their spawn points are blown up. Then the game would end once the team is finally killed off, or time runs out.
Also, for multiplayer, I think the ranks should be like halo reach, except credits can only buy you armor, and EXP ranks you up. I also agree with the statement saying that the gun your Spartan holds on the start menu should be customizable, different weapons costing credits. Also, one more thing for multiplayer armor: MAKE RECON A CHALLENGE TO GET AGAIN. And also don't make crappy helmet attachments a complete rip off.
As for campaign: I just think it should be a long, exciting experience that keeps players challenged and hooked. Also, have some silenced weapons too.
All catergories: bring back the carbine, brute shot, missile pod, smg, and the multiple grenade options, but keep the DMR, needle rifle, concussion rifle, plasma repeater, and plasma launcher. BUT FOR THE LOVE OF GOD GET RID OF THE FOCUS RIFLE. Also, include troophogs and brute choppers. I also think halo 4 should come in 2 disks: one for campaign and offline firefight, one for matchmaking, forge, custom game, and theater. Well, I think thats all