TL;DR - The ebb and flow of map design, weapon and vehicle sandbox is what makes Halo great, specifically objective game flow regarding map and spawn design. Get ranked in and put guests out of ranked objective.
Fuck objective glitches, that's not skill at all IMO e.g. flag bouncing on Colossus, flag launching on Valhalla, throwing a neutral bomb out of the map etc. All of which were actively removed from matchmaking at every chance (it just took ages to get done). Fun yes but very short lived and not able to retain population or attract newer players to objective.
I'm all for objective mechanics generally being far more enjoyable in Halo 2/3 but the progression of anti-spawning kill farming and objective holding needs to get to the point where objective centric elements always out score slaying.
Bring back H2/3 assault, bring back 1 flag gametypes, reintroduce ricochet over stockpile or head hunter and have really skill/team based objective back at launch with a quality rank, no guests in ranked and matching system in game.
Things like warthog riding on burial mounds were a fantastic opener for objective rushes e.g. ride on a hog carrying the bomb straight to the arming location or in 1 flag ride the hog then launch yourself straight out the base window while grabbing the flag. The enemies had every chance to stop you but the teamwork, dexterity and timing to pull these sorts of things off was insanely fun and rewards.
How about Zanzibar 1 bomb where you essentially have the usual Bungie rule of 3 to go Froman, straight up the middle or bridge tower? How about choosing a warthog rush with the bomb carrier over an on foot assault? A series of perfect setups each with the attack/defense balanced e.g. laser to counter rushes. The assault carrier had plenty of routes/obstacles to make any stealth or team brute force runs as you wanted. Maps like Headlong 1 flag or 1 bomb again provided the routes, stealth or vehicle/map control to really enable objective.
For me objective has always been more about seriously high quality map design and play testing with sections of the maps appearing as mini stages if you will e.g. Valhalla attack/defend the base then get over the hill as a separate mini stage or zanzibar the base, the wall, the beach and they worked in terms of flow in both directions. I'll take maps akin to H2/3 objective over anything Reach or 4 produced. The saddening part of 4 is the current sandbox and some of the maps would play so fucking great with 1 flag or 1 bomb. Instead we got noob friendly flag waypoints, no dropping and auto-pickup.
Even with those elements how did the design team not want to put in 1 flag? Honestly at a design level ask yourself is it easier for newer players to understand 1 flag or 1 bomb over say 2 flag or neutral flag? To me the answer is obvious even with 4's accessibility design goals, round based objective is so much easier to understand for newer players and helps the random teams play together, they have automatic roles to play where a dynamic game of 2 flag takes skill, timing, practice, awareness and communication irrespective of H2 or 3 or 4's individual mechanics.
When you look at skill and team matching objective is even more lopsided than slayer, to keep players coming back spawn killing and objective holding has to go. I'm all for skills/teams being rewarded and a decent skill gap but it simply can't reward the 1% as a huge % simply don't stick with gametypes or less regular teammates to get good at a playlist. Literally the top teams destroy playlist populations are for the other team it's just not fun being on the other end of the host, the regular team and being spawn killed for 10+ minutes. I'm no slayer expert but I imagine much of those reasons are where MLG has died off population wise as objective has with each iteration of the game.
The game timer has to play into the scoring of objective games far more while reducing spawn killing e.g. imagine getting 3 caps within the first 3 minutes then your entire winning team receives magnified rewards. This should be far in excess of objective holding and spawn killing for the remaining 12 minutes. Imagine a personal best for number of flag steals per game, flag caps per game, time to win in each objective gametype. The more time left the greater the multiplier and it works for bomb, neutral, 1 flag, 2 flag etc. It drives teams and players to want to play the objective, allows for stealth and reduces objective holding.
Just look at any gametype in Halo that provided rewards for rank or progression systems, the masses and especially the hardcore dedicated flocked to it. How many farmed XP in Firefight in Reach? How many boosted ranked games in 3? My point is make objective something players and teams want to accomplish and quickly.
K/D should have a reward in objective, slaying is still important but it has to take second place with regard to scoring and objective mechanics.
Many of the ideas in Halo 4 objective are nice, the idea of scoring and other medals are solid ideas and help promote this for objective e.g. flag assist, flag defence, driving a flag carrier home etc. Provide more of these sorts of key elements and reduce the noob friendly crap to really deliver kick arse objective games please.
Many of the glitch or unintended elements of previous games should become newer mechanics e.g. flag window passing on isolation or flag passing on sidewinder or flag bouncing on colossus. The point is these mechanics are what the design teams should progress forward and enable for all players. I'd prefer to see that sort of resource investment over an attempt to make objective more accessible, it also points back to all Halo really needs is high quality map design, weapons and vehicles that enables gameplay.
Clans + in game rank + objective CE + H2/H3 + key scoring elements from H4 + H4 gunplay/movement + high quality objective based maps - H4 watered down objective = hella good, hella fun and rewarding as hell for new players or regular veteran teams.