Imagine this; A FPS Massive multiplayer online game set in the Halo Universe. Just without the PLAY TO BE COOL PAY TO BE AWESOME ← Just no on that. Just no. Games should not be dictated by pocketbooks. You combine everything Halo; From every weapon, vehicle, faction. Break it down into faction wars. UNSC,Covenant,Flood,Forerunner maybe? Put in a credit system where you can unlock weapon load outs cheaply but the aspect of unlocks has no Statistical effect on gameplay like a unlock gun is stronger this gun because its stats are higher. No its like classic halo game play.
Each gun has its set stats. Lets say I get credits I can unlock a Plasma Repeater or a fuel rod cannon. These weapons have no special boosting stats. They just function purely how they functioned in the game. Though even more cooler to take timeline in to aspect. You unlocks start you on Tier 1 or Halo Combat Evolved or Halo Reach time line. As you progress through unlocks you unlock higher tier weaponry that are more advanced dictated by the timeline of the Halo Universe. Like you get Brute plasma rifle later on.
Same can be said about armor permutations or flood evolution forms. Though for simplistic sake of balance you can make Flood and Forerunner random A.I Controlled factions that break loose in a FPS environment. Which forces playable factions like UNSC and Covenant to halt their maiming of each other and join forces to deal with the initial threat.
Even special call in abilities can be done like the Planet side vehicle system but more so not from a stationary facility. If you feel safe enough in a general location you can call a Pelican to bring you a warthog in the field. So you and your friends could mount up, or a Wraith to bring in a Spectre or Brute class Prowler.
Even more so on the MMO aspect you can have battles across the stars. From planets, Rings, space stations, ect. So this brings in a space combat aspect. Where as if a player wanted too. They could pilot a UNSC frigate and duke it out with Covenant Banshees, Wraiths, Frigates while deploying their own form of counter like long swords and pelicans or other space faring UNSC vessels. Combine that with Real time aspect. You have a never ending battlefield opt to changing.
Also don’t forget fan made content like Forge. Players can utilize a even greater forge system to attribute to the game. Designing battlefields which can be opted to Game Developers for choice in implementing into the battle field. Call these [FORGE worlds]. A blank planet where people have the option to contribute to its battlefield construction. Hell even allow players to submit weapon/armor/and special equipment design concepts. Allowing for the old Halo CE Modding aspect but through a controlled and organized system.
As for the Faction Player system. Take UNSC. You can play as a UNSC Marine, ODST, Or a Spartan and command the appropriate resources to do so. Feel what its like to be in the boots of each individual role. Vise verse for the Covie. Ever wanted to be a Brute? or a Hunter. What about a bugger? For some player roles will dictate what gear you get but there is a core role like Spartans and Elites which in the classic halo game play allows you access to everything being a modular role but in the same instance dictated to certain things you can’t get. Like a Hunter Fuel Rod. It would be silly to see a hunter with a plasma rifle or the mounted cannon on a hunter carried by an elite.
Other than that; If anyone likes this idea feel free to debate on game features or something you like to see expanded in this idea.