Witcher 1, 2, & 3. My all time favorite RPG by far. And that was BEFORE Witcher 3 which deserves every accolade you have seen it be given. Make a decision and see the impact 10 hours later. End results that really depend on decisions made in game. I can't say enough good about this series. Just play it an enjoy the way a RPG should be. There actually is an overriding story arc that starts in Witcher 1 and goes all the way through. (Thank Septkowdki I think. Not that he wrote the game (he didn't), but there is an arc in the Witcher books that the game people were wise enough to pick up on.
Witcher 1 actually holds together pretty well even though it is about a decade after its release. Any one of the three is fine but playing them in order is especially tasty.
Get it from http://gog.com for very good prices. Also, get the GOTY Witcher 3. The DLC you get for the extra 5 bucks is over 40 hours of game play.
The soundtracks seriously rock as easy listening music.