Headshots are great, but Halo 5 is all about Backshots. Halo 5 is manageable when on normal or even heroic difficult. But when you crank things up to Legendary, it's a difficult ball game.
In this video, The Junglist has a few suggestions on how to best approach Halo 5: Guardians when things get tough.
It's funny how Halo has evolved. Each game brings new weapons, different enemies and they all have to be approached a little differently. Compared to most first person shooters, there's actually a fair amount of problem solving in Halo. That's why this video is so helpful. Have a gander!