As someone who has played Halo since the very beginning I highly suggest that you play Halo 1-4 first if you want a good firm grasp of what's going on. I'm sure Halo 5 will stand on it's own just fine, but the subtle nuances may be lost on you. Like what exactly Chief has been through. His struggles and challenges. Everything he's sacrificed. It connects on a more emotional and human level when you know the Chief as well as many of us do. Besides the campaigns are awesome and a lot of fun. Books, comics, movies, games, short stories, and audio "blogs" like Hunt the Truth - there's no shortage of material for you to absorb. :)