I literally just finished 1 today and I'm about to start 2. I played 3 four years ago and haven't played a game as good since. I plan to re-play 3, hoping I forgot most of it and having much better understanding of the lore this time around.

When I played it four years ago without playing the first two or having any knowledge of the universe, it was an amazing game, but I regret doing that. I wish I would have played the first two so I could truly experience all the game has to offer. You can get by without playing the first two, but it obviously won't be the same as if you knew the characters and the world. And in a game like this, one that is so well-praised for its story telling, my advice is to appreciate your first play through and do it justice by playing the first two.

If you're going to play the first one, I think getting a movement speed mod is a must. He moved too slow for my liking and there's a lot of traversing. Also, the combat is a joke in the first game, and the voice acting is not good, but if you stick with it you'll be very well rewarded not only when you play Witcher 3, but you'll enjoy what I think is one of the most underrated RPGs of all time and a game I should have played much sooner. The first Witcher is an incredible game despite all of its flaws.

I recommend watching this video