I'm a huge fan of the changes between Witcher 1 and Witcher 2. In the first game, you could level up only the strong and group style combats and be completely overpowered in every fight you ever go into. The group style made hoards of enemies a complete joke, while the strong style made bosses unable to even hit you once.
In this game, you have to really strategize every hit. It's a whole different ballgame for sure, it took me a few hours to really get used to the change, and I love it.