I would recommend playing the games if you enjoy the series, since they are both great games. If you are an achievement hunter though beware - ACB has a few achievements that are kind of a bitch to get.
You will probably have to boost a couple of the mp achievements (unless you are awesome at mp and/or prepared to dedicate countless hours to grind to Level 50). Also, there is an achievement for 100% sync on all missions and you will probably end up repeating some missions a few times (or a few hundred
times, in the case of "Hell on Wheels"...) before you get 100% sync.
That said, I still recommend playing the games to see the storyline for yourself. It's much better than reading about it, IMO.