Sadly the Witcher 2 went with the button mashing combat style, abandoning a feature that set the first game apart. Just pushing the mouse button rapidly is all you need to do now
I didn't find this to be true at all... whenever I just tried to mash the mouse button I was very quickly killed. Instead I had to think carefully about when to strike and I had to use lots of dodging. I was using the highest difficulty setting though; you might try that if you haven't yet, and see if you like the combat any better.
I agree that the system in The Witcher 1 was unique, but in the end I felt it made the fights rather boring, even at the highest difficulty setting. There were tactical considerations before the fight, like whether to apply an oil to my sword and which potions to imbibe, but the actual fights were very simple. Just pick the right sword style and then click at the right times. It felt like I was just watching the fight instead of actually guiding it, and there weren't really any tactical considerations other than continuing through the sword sequence. I guess I might occasionally throw a sign in, but otherwise it was just timed clicks.
In the Witcher 2, by contrast, I was worrying about positioning, parrying, waiting to strike so as not to leave myself vulnerable, throwing bombs, and using signs more often. I did kind of miss Geralt's crazy kung-fu sword mastery, but I found the combat system was far more satisfying to actually control. It did take some getting used to though.
EDIT: I should clarify that I was playing on Hard, not on Dark Mode... I played before the 2.0 patch that introduced Dark Mode.