Customization sucks. At first you couldn't even use the items you unlocked or purchased on different cores. It's still a chore and you can barely unlock items for free.
In order to progress the battle pass or timed events, you are forced to play certain gamemodes or use certain weapons. You don't get xp based on match performance, so you have to play how the challenges make you play.
We're approaching the one year anniversary, and we're still only in the second season, with season 3 being delayed to March next year. Since release, we only got 2 new maps. That's it. Yes, some new playlists, but most of them should have been in the game since launch. We still don't have forge, which has been delayed AGAIN
The gameplay itself is fun and well-balanced, but the game is riddled with desync issues. Also, the weird skill based matchmaking system that's in place makes social matchmaking feel too sweaty. As for ranked, the games feel rigged to make sure you have about a 50-50 winrate. There is no fun in grinding for a higher rank because you are punished for doing well.
That's only the multiplayer. The campaign is OK story wise, and the artstyle is really cool. But for some reason, 343 decided Halo needed to be an open world game. Fair enough, they tried something new. But the trade off was not worth it.
Everything looks the same. You have the outside gameplay, which all looks the same. Just some generic grassy areas with rocks and trees. Then you have some Banished structures which are cool but repetitive, and Forerunner structure, which again, all look the same.
As a result of it being open world, there still is no co-op and you can't replay missions. Split screen has been ditched, even though they promised that every Halo game will have splitscreen. They kept that promise for all of 0 games.
And don't forget the fun glitches that they fixed for absolutely no reason. You were able to fly the Pelican. Nope, too much fun. There was the tank canon. Gotta fix that! To be fair, they did patch that back in after community outrage.
343 has dropped the ball on so many occasions and their communication is piss poor. Don't just brush off all Halo fans for being toxic. Our patience has finally run out after more than 10 years of having hope for 343