It's not the best Halo game. Frankly it's hardly a Halo game. A ton of the new gameplay was lifted off concurrent FPS games like Far Cry and Titanfall. Putting it side by side with the others makes it clearly stand out, not in a good or bad way, it's just very apparent.
The campaign was a let down. I'll explain it this way, imagine never seeing a Marvel movie then watching Avengers: Engame half way into the film. A ton of things happen prior to the story and, taking a page from Fallout 76's book, they fill you in via audio logs. Everything is very jumbled in the beginning and even after finishing it, I still have hardly any idea of what just happened.
But I did enjoy the humanizing moments Chief experiences, having him interact with a non-soldier was very welcoming. But those few moments aren't enough to make a well rounded plot. They clearly wrote it around him and the Pilot without anything else in mind, other than the off brand Cortana who gets in some one liners.
That's said. I loved the fast gameplay and new weapons. The Banished are a fresh new enemy force to fight against and they feel far more aggressive and desperate than the covenant.
It's not a bad game, in fact it's a very refreshing FPS, probably one of the better ones that have been released in the past year. But as a Halo game, it's an insult.