People cheat in almost every online match I play.
Just to name a few examples:
Unshielded headshots not killing players,
Headshots with sniper weapons not killing players,
Melees to the back not killing players,
Power weapons and weapons in general doing little to no damage.
Here’s an example with the power weapons:
I attack someone with a Gravity Hammer, it doesn’t kill them.
Later in that same game someone comes after me with a hammer, they use it the same distance from me if not farther away than when I used it against them and it kills me instantly.
If I wanted to put up with this garbage, I’d play PvP in Destiny.