I really liked the careful preparation of the 1st game. You had to find good booze for your potions, talk to the old people to gain knowledge about the beasts. Also the "romance" stuff was very much like in the books.
W2 was better in many ways but it got worse as the story went forwards. I liked more of the closed story of the W1 instead of the "saga" approach of the second one.
Witcher 1 had great story and it set the world better than the W2. Also Witcher 1 feels more like a witcher kind of adventure - at least comparing to the first book stories. I doubt that the choices carry over in any meaningful way.
How about the books? Sword of Destiny was great introduction to the world of the witcher and the Last Wish has important chapter relating to the W3.