This will be a LONG thread but the TLDR is Halo Infinite is a great game that is being stunted by issues in too many areas in the game.
Now I will go into detail about everything I can think of that I personally believe would change Infinite for the better:
CAMPAIGN:
Not much needs changing here aside from Network Co-Op, Splitscreen Co-Op, Mission Replay and hoping for more story in the future.
FORGE:
Forge looks great. Havent seen any evidence of PVE stuff in forge so if that isnt in the release version of forge hopefully that can be added in the future. All forge needs is for the file browser to be fully functional and a good customs browser and that will keep the social side of Infinite thriving indefinitely.
FIREFIGHT/PVE MODE:
I believe Firefight (or some variation) should return to Infinite and be expanded upon massively, I really think it could become Halo’s version of COD Zombies. They could implement an Easter Egg quest, boss fight and ending cutscene to every map. They could expand it in many ways.
MULTIPLAYER:
Ok this is the big part that needs the most improvement.
RANKED:
Ranked needs more variety and playlists to choose from. Here are all the playlists I would ideally like to see in the Ranked offering soon:
Lone Wolves: 6 Player Ranked FFA
Doubles: 2v2 Ranked Slayer
Arena: 4v4 Ranked HCS (Oddball, Strongholds, CTF, KOTH)
Slayer: 4v4 Ranked Slayer
Attrition: 4v4 Ranked Attrition
Featured: Weekly/Monthly Rotating Ranked Playlist (4v4 S7 Snipers Only, 1v1 Slayer, 6/8 Player FFA S7 Snipers, 4v4 SWAT Slayer, 4v4 SWAT Attrition, Ninja Slayer, etc.)
The playlists that absolutely need to be added are Lone Wolves, Doubles and Attrition. Lone Wolves gives players a way to express individual skill as a solo player. Doubles allows you to play as a smaller scale team and is still good for solo players compared to 4v4 modes. Attrition is a great mode and currently is only available in Quick Play. It deserves a dedicated playlist and being quite an intense mode should have its own ranked playlist and it also gives more variety to ranked.
The matchmaking in Ranked should just be based around matching the same ranks together rather than based on tightly matched using the hidden MMR stat.
Also CSR shouldnt hold you so tightly tethered to your MMR stat. It should allow you to climb as high as you can before you start getting hit back down the ranks if you cant keep up. A more natural progression through the ranks should be allowed to happen, which is why the placement cap should be Gold 1. Creating more of a natural progression while climbing the ranks allows people to feel like they are making good progress when they play well and fairly punished when they dont.
The CSR should not sky rocket you to the rank the MMR stat thinks you deserve then grind you to a halt and pull you sharply back if you stray too far. That isnt fun and doesnt feel rewarding even if you play well.
Lastly in Ranked playlists I believe you should only spawn with one frag grenade rather than two. This will promote more scavenging and alleviate some nade spam problems without any direct nerfs to grenades. Having 4 grenades flying at you at the start of every game will feel a lot better than 8.
SANDBOX:
The sandbox in Infinite is actually very good but I do think some minor changes could improve it.
Plasma pistol feels pretty weak. The tracking feels inconsistent and the gun just overall feels weaker than previous games.
S7 Sniper feels pretty bad in Infinite. The glare definitely needs removing or at least toning WAY down. The bloom also needs removing or toning WAY down. The zoom of each scope should be lower. Making the normal scope 4x zoom would massively improve how it feels.
Gravity Hammer feels awful with how slow it is, it needs to be fast like other Halos.
Battle Rifle could potentially have SLIGHTLY slower bullet velocity. It should NOT feel slow like Halo 3s, but slightly slower would help for BTB. The BR should feel exactly the same in Arena range maps but for the extreme BTB map ranges you should have to lead your shots a little bit. That way you could spawn in BTB with the BR.
Bloom overall needs to be removed or toned WAY down for pretty much all weapons and the drop weapon animation should be the same speed as switching weapons. Its making too many combos too strong.
EVENTS:
The events could do with some improvements. They are fine but could be much more exciting.
The Christmas event for example could be massively improved. Do what they did in Halo 5 with adding snow to the maps and have snowflakes falling during gameplay. Then go further and add some Christmas lights, trees, presents, decorations to the maps too just to make the gameplay feel more Christmassy. Make the armour more uniquely Christmas themed too. Maybe add some snow markings to event armour pieces, add a Santa hat to the helmet, have Christmas style armour effects and kill effect animations, have armour pieces wrapped in Christmas lights, etc. And make a unique snowball fight mode for the Christmas event or something.
Going big and unique with the events builds more anticipation for them throughout the year. Do the same with a spooky theme for Halloween, Easter theme, Summer theme, etc. Games like Destiny and Call of Duty have done this well in the past so take inspiration from them.
SOCIAL:
Social will be hugely saved by Forge so it is more important for Social to cover the basic areas rather than needing to cover everything. There could be a few standard playlists like Slayer, Rumble Pit, Last Spartan Standing, BTB, Quick Play, Doubles and SWAT. Then have a couple rotating rotating playlists like Fiesta, Team Snipers, Shottys and Snipers, Low Gravity, Infection, Grifball, etc. Whatever they want to add similar to how MCC handles the Social Playlists.
PERFORMANCE:
This is pretty simple the Desync needs fixing ASAP. Connection problems need fixing. Crashes need fixing.
MATCHMAKING:
Matchmaking needs to be looked at and re-evaluated. The social modes need WAY looser SBMM. Use the principles of the Halo 3 matchmaking where they wanted to provide a variety in the social modes between closer and looser matched games. Good connections should be prioritized at all times. Also give the power to the players to choose how they want to matchmake like in previous Halos. Give people the choice between prioritizing Skill Prioritized MM, Connection Prioritized MM, Region Prioritized MM.
PROGRESSION:
The game needs to offer a better sense of Progression. The new Halo Waypoint Service Record is great, but needs to be in the actual game. It also needs to be viewable to anyone view in matchmaking/friends lists.
The game really needs an XP based Account Level. This could be a military rank like Halo 3. This could be a title like Halo Reach. This could be Spartan Rank 152 (or even higher) from Halo 5. This could literally be anything as long as it feels rewarding and feels like good progression. Just needs something to keep progression alive during game time and to show off on your service record.
CUSTOMIZATION:
Customization is actually pretty decent in Infinite at a base level but it has too many unnecessary restrictions. Cross core is necessary to make customization better to start with. Coatings should be available across all armour. Buying things from the store needs to feel worth it so ideally they need to be available across all cores. We also need stuff like animated visors, animated nameplates, etc. like the MCC offers. Maybe even animated weapon and armour coatings if possible. Coatings need to be much more than basic colors otherwise that just feels like something taken away from us that we had in previous Halos.
CONCLUSION:
That’s pretty much everything I can think of. It may seem like a big list of demands but really it comes from a place of seeing how much potential Halo Infinite has and wanting it to succeed. There may be more I haven’t included but a game can ALWAYS get better and its important to keep pushing 343 to make Infinite the best they can.