The single player campaign is a 6/10 for me. The first hour or so before you get into the open world is a boring slog. Some of it looks good but some of it looks really bad. The animations on some of the enemies looks good but the cutscenes are pretty horrible. The main bad guy is cliche and seems very one dimensional. I don't really care about his threats, who he is, or anything about him.
Once you get outside it does get better but it is just not that great. The open world looks okay but things in the distance look bad, some of the effects are terrible (tire tracks), and it just looks like a game from 4 years ago. I also find pilot annoying, he just complains the whole time and the open world is just okay. When I'm playing it I just keep thinking is this game better than other open world FPS games and I keep coming back to the same answer, no. It doesn't look better, the world isn't better, the story is weak, etc. If it wasn't Master Chief I think people wouldn't be giving this game anything above an 8, the nostalgia is definitely boosting a lot of these scores.
I would say if you aren't invested n the Halo universe then you're not going to love this game. You'll probably have a decent enough time but it really isn't all that. Don't trust anyone who's giving this game a 10/10, they have rose tinted glasses on in my opinion. Maybe the Xbox One and Series S held it back. I'm running it on a RTX3080