I like the Witcher 1 and Witcher 2 both, but for different reasons.
Witcher 1 has the best story of any RPG I've played in the last 10 years. The characters were also spot on, the quest lines interesting, and the finale mind-blowing. Complex out-of-combat mechanics. Unfortunately, the combat is mediocre (or maybe just poor).
Witcher 2 has some of the best graphics of any RPG I've played as well as much more exciting combat. Unfortunately, everything else was reduced in depth. The story is kind of a wash. The quests more boring. It was a lot more focused on immediately rewards (combat and graphics) rather than plot or characters.
Overall, I prefer Witcher 1, but I also enjoyed 2. I'm excited for 3, although I expect it to be a lot closer to 2 than 1. The quests do seem a bit more interesting, from what I've seen.