Unlike the easier and simplified combat system in Mass Effect, you need time to learn the control in the Witcher. You'll get use to it eventually with higher satisfaction, felt more involved in combat, than Mass Effect.
As PJ said, changing up the options during battle makes it very immersive. Not to mention the sometimes needed tactical planning to beat those really tough groups.
I agree on this one too, you must try different things to have a chance to enjoy the fights.
But I also agree that the fight system design have some big holes and you could clearly just chain clicks, almost never move and almost never change style fighting or almost never combine sings and sword. Just few potions and/or oils before some fights and systematic clicking is enough for most fighting. Gothic 3 had a similar problem but with increased effects on gameplay.
My problem with G3 was that if the opponents had no missile weapons, you could kill a potentialy infinite number of them by repeatedly hitting the LMB. The Witcher is a bit better than that ;-)