Although Witcher 1 and 2 might seem a bit clunky to play, they are worth it in my opinion. Certain decisions that you make during Witcher 1 will carry over to Witcher 2, and then same from Witcher 2 to Witcher 3. If you play Witcher 3 directly, you get to pick some choices but if not familiar with the Witcher universe then it just a guessing game. So yeah, I would recommend you playing 1 and 2 first, the cost for the games wont be much anyway. Just compare the prices on Steam and GOG before you commit.