From what I understand the game takes place after the books - so it's not based on any of them.
Combat in the Witcher is not just clicking at the right time. You also get to try evade, dodging and leaping over enemies. A good position can win you a nasty fight. Not to mention the style switching.
Each sword has three styles - fast (For quick enemies), Strong (for armoured enemies) and Group (For lots of enemies). Right sword + right style can give you a fairly easy victory in many fights - but you may have to switch both in a hurry.
