Halo 5 launched with a lot of missing content and was a pay to win game with its REQ system. If you haven't been playing continuously you won't have any of the good weapons and equipment.
Furthermore, the game is catered to competitive players instead of the larger casual base and in doing colour and texture pallets have been sacrificed.
Lastly, the campaign is quite a disappointment and it feels like 343i forgot to hire writers for both the story and character development.