It won't really ruin your enjoyment of Season 4, but I would recommend it for the flashbacks to the Scorpia Shipyards attack, and the First Cylon War. You also see Admiral Cain was a bit of a hardass from the beginning, but she also suffered quite a decline, and betrayal. So, it does make her actions in Pegasus
and Resurrection Ship
more understandable, but still not forgivable.
The scariest thing is, Adama seemed to be set on the path she initially was taking after the attack, were it not for Roslin's convincing him to run rather than fight (although I could never see Adama doing some of the things she did).