I'm think I'm going to do all 4 campaigns for the first time before delving into MP.
Question: I know people hated halo 4 mp... Is the Sp hated as well?
Story is very poorly told, especially if you don't read up on the lore and the new expanded fiction. Believe me if all you've ever played is just the games, you'll be confused as well.
Additionally, the gameplay is very linear with a lot of go here, press this button, cleanse the enemies move on and repeat. The enemies are also damage sponges. One enemy flies away quickly, another can crawl on walls or swarm and the promethean Knights are the worst. Take a lot of damage, can teleport away, or have 1 hit kill weapons. You're in for a rough time on heroic or legendary.
But the cinematics are top notch, and people really loved the story between Chief and Cortana and how they humanized him. So it's definitely worth playing through, especially for Halo 5.