Having given it little to no thought but with some mildly changed, less-OCD tastes than last time, I think I'm going to try and get down what I'd want out of a competitive (but still fun) multiplayer sandbox. Weapons, anyways. Dunno about vehicles.
Loadouts: Magnum / AR / Either 2x or 1x Frag starts across the board. Four "classes" available, with the sole difference being an armor ability.
AAs: Sprint, a buffed Thruster (pretty much a single-use per charge Evade), Jump Jet (double jump), and Halo 4's Hologram.
Grenades: Frag / Plasma / Firebomb / Promethean Pineapple
The Firebomb would have a slightly larger radius and less damage output, but with damage that increases closer to the epicenter you get. It's meant to be a denial-of-entry / suppression grenade now, with it only making kills on direct hits / walking through the entire diameter of the fire.
The Promethean Pineapple would just be some sort of Pulse Grenade-ish thing with added stasis functionality.
Weapons:
Magnum (Halo 4 version, but with Combat Evolved levels of feedback)
AR (Halo 4 version)
Plasma Rifle (Combat Evolved variant)
Plasma Pistol (Reach Beta variant)
Bread-and-butter weapons located throughout the map.
Battle Rifle
Carbine
Light Rifle
The three precision weapons would have roles very similar to their functions in Halo 4 Turbo, with the key difference that they don't show up in loadouts - instead, one of each type spawns in the general perimeter of opening spawn or the team's base. In a traditional 4v4 environment, this leaves one player with an immediate drive to locate additional support, such as a power weapon, powerup, or vehicle, even in Slayer modes.
Needler (mix between Combat Evolved / 4 versions)
Shotgun (CE version; favors range over Halo 4 version's evident "bulk")
Sentinel Beam
Low-level power weapons. The Sentinel Beam in particular would replace the DMR not only as an anti-sniper weapon, but as a vehicle stripper. The Sentinel Beam would gain a unique property in that its beam actually gains power over distance (capping at about 200%, maybe) despite lacking a scope with a power level between the Halo 2 and 3 editions, meaning that using it to suppress a sniper would be doubly effective.
Energy Sword
Grenade Launcher (added Sticky Det. functionality)
Railgun
Mid-level power weapons.
Rocket Launcher
Plasma Launcher
Sniper Rifle
Beam Rifle
High-level power weapons. UNSC versions are more deliberately anti-infantry, while Covenant are anti-vehicle.
Powerups: Camo / OS / Damage Boost / Speed Boost, bare minimum. Some extra powerups could replace oldie-but-goodie Armor Abilities / perks / etc.
I think that leaves the total at 17 weapons, not including grenades. I feel like I'm forgetting some, though. There are also a few wild card ideas I had like the ONI Hard Sound Rifle, a "cluster buster" Promethean Revolver / Scattershot combination thing, and of course the Gravity Gauntlet, but those would be superfluous.
