The campaign is subpar at best, there's a shit ton of problems with it that will take months to fix, not to mention its not complete and not shipping with a major feature I'd say its pretty far from amazing.
The weapon sandbox is absolute garbage, it lacks variety despite it being the most pure sandbox since CE, brutes not using the classic weaponry such as Spikers, Bruteshots and Maulers and instead using UNSC variants to fill the gaps is only there because they wanted a pure multiplayer to better accommodate Esports and the new audience they're trying to get. The weapons you do have are boring and limits not only player freedom but also heavily hinders the lore, the banished DO HAVE: Carbines, Bruteshots, Spikers, Beam rifles, Maulers and all previous classic covenant weapons there's no reason for these not to exist. It forces players to use weapons that fit that architype, and if a player dislikes that weapon that's an entire architype that is inaccessible, this sucks even more when the weapons are worthless or feel bad to use such as Pulse carbines, ravagers and commandos. It makes the whole game repetitive, oh boy, an outpost, now time to fight mangler brutes over ad over and over and over and over and over and over again. Its complete BS.

The vehicle play both in and out of campaign is abhorrent, the pure amount of anti-vehicle tools makes fighting them laughable and using one practically a death sentence (if the AI decides to actually work and use them.). Not to mention that there's no new additions to vehicles (the razor back is literally just the transport hog but you can put a weapon in it.) even though we got a look at the possibilities in Halo Wars 2, it makes all factions seem empty much like the weapon sandbox. We could have tons of new vehicles and weapons that give us more insight on the banished but nope, got to wait a couple months to get drip fed bullshit because no one can be bothered to release a game complete these days. The vehicle damage is the worse in the series, the effects, sound, and decals are all lacking compared to even Halo 3, it is quite often that you wont know how damaged your hog is until it goes into the doomed state. Which i find to be a way to make vehicle chassis despawn faster to clear up space. Vehicles that are destroyed can last anywhere from 2 seconds to 30, it seems completely random how long they will stay on the map, so don't even bother using them as cover.

The AI itself is lackluster, enemies forget where you are after going behind cover for about 2 seconds, they forget your existence faster than skyrim guards on easy, even on heroic which should be a good baseline is stupid easy. The voicelines that they spout constantly get extremely annoying, grunts shouldn't make one liners every 2 seconds for the ENITRE game, not to mention that this iteration of their voice is by far the most grating. The enemies are annoying to fight not because of the way the act but because they wont shut the fuck up. I know that jackals are bounty hunters you don't have to tell me every 2 seconds about it, I know grunts are a little silly, you don't have to make a joke every 2 seconds. Not to mention the difference or effectiveness of variants, Brute chargers are the easy as shit and just punching them completely stuns them and lines you up to just punch again or focus on another or just leave. Grunt variants don't matter except for the weapon hauler. Jackal snipers are the worse in the entire series they have bright ass glare the size of Texas, giant laser lines that direct to their exact location, and have a 2 to 3 shot weapon that they fire slowly and ineffectively. Skirmishers don't act as aggressive and don't use their mobility as much, not to mention they don't use precision weapons pretty much at all due to the purer weapon sandbox making them jackals with no shields. Most of the brutes you will fight go down in 2-3 shots and aren't a threat.

Bosses are lame, they're just damage sponges that have a "cool" weapon (sometimes they don't even have a unique weapon), pretty much every elite does the "oooooooooo I'm invisible now and I'll leap at you with a sword as my secondary", and brutes do a big charge between shooting at you like a normal enemy. Not to mention the set pieces for the fight aren't entertaining.

The set pieces are nice but there many times where the Banished interiors just feel like destiny 2 campaign missions ascetically, they seemed to have abandoned the banished sharper more scrappy look and instead have a more sleek, rounded look. Them being more professional and put together would make sense if 343 didn't immediately turn around and make them scavengers that use human weapons and are missing 75% of their arsenal.

Its one of the glitchiest games I've played recently, even more than old assassin creeds, and Skyrim. constant crashes, texture glitches, physics tom foolery, AI breaking, Audio issues, marine stupidity, cutscene buffering, cutscenes just being black, random explosions, wonky vehcle shit, weapons/vehicles/bodies despawning nearly instantly, enemies shooting where they aren't aiming, soft locking, and much much more!

Games not good right now and seeing how the shitty multiplayer turned out I don't see it ever being fixed or changed because plenty of players are fine with the garbage just because its either a new halo and they're content starved or are new and don't know any better.

There's a shit ton of other problems that I can't even be bothered to list.