Do you mean the multi?, well to practise for an upcoming sequel such as a CoD game you should really play the older game without any bonus perks or class abilities unlocked, basically go for stripped out pistol user to get use to the controls without the crutch of your favourite perk.
It eases the transition from game to game because your honing your base skills, not exploiting a bonus you've gotten used too. You can then build on that for the new game once it comes out.
It eases the transition from game to game because your honing your base skills, not exploiting a bonus you've gotten used too. You can then build on that for the new game once it comes out.