I'm new to the Witcher series and wonder if I should spend time going through all of them. I read that the story is somehow related and there's even ability to import saves from previous parts into the next ones. I had a similar experience with Mass Effect, where having started with second piece I eventually replayed the game starting from ME1 for a much more rich experience when I could understand story behind characters from ME1 (and later ME2) showing up in the game.
Thus ultimately my question is, how the three Witchers are related in terms of story (NPCs with history, locations, quest decisions etc.) and if how much time will I have to devote to parts 1 and 2 if I only consider the core story-line of those?
There's a related question, but it only considers the first two Witchers.