You don't need to play Witcher 1 to understand Witcher 2, though it might help. I played 1 before 2 but I still felt a little lost at the beginning of 2 because the world and the story are pretty complex. Witcher 2 does have a journal with character bios and stuff to help you make sense of it. The first game is pretty good and some of the choices you make slightly affect the sequel, so you might as well try it, but if you can't get into it it's fairly safe to skip it.
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My fingers -- ALIVE! And threatening me with -- DEATH!