Stop thinking of this as taking ideas from other games. Think solely of this as what has been offered in previous Halo games. CoD did not patent or copyright the use of a shield it is not stealing in anyway. Think of it this way, you can use a knife when you melee with a single weapon. If you have 2 however you can only melee using the weapon itself (less damage then a smooth or serrated blade). Holding 2 weapons at once should decrease or totally eliminate melee and should double recoil of the weapon. There should not be any extra equipment use while dual wielding such as grenades or some sort of armor power-up.