The important part of Halo is the storyline of the entire halo series campaign evolving around Master Chief, Cortana, and the Rings.
-Look back at Halo 1, it is mostly developed on your relationship with Cortana and the rings. As you go through the gameplay, your bond with cortana tightens, as it does throughout all the Halo's. The rings however, are also developed about how 'you needing to protect it is the utmost importance, as humanity deponds on it,' and that the rings aren't what they appear.
-In Halo 2, the same exact thing happens, except at the end you lose Cortana on High Charity, leaving her to fall prey to the Gravemind, one of the reasons why the rings were created,
-Halo 3, in my opinion, is the 'Real' ending in Halo, because of the fact that the end of Halo you got Cortana back, the rings were 'Mostly' deactivated, and a treaty between Alien Races was built.
-Halo 4, I think was very dramatic but the storyline in my opinion wasn't great because it was just so wierd how they introduced the Prometheans into the campaign like they did. I felt they rushed into it too much, and the way they ended the game like that was just a big emotional disappointment.
