After I had read the two books, the Last Wish and the Sword of Destiny and played the Witcher 2 Assassin of the Kings, I decided to tackle the first Witcher game. After beating the game, I was happy that I decided to do so. The World in the first game has better feel to it, and the main and side stories are more like in the books.
However most of the changes they made for the Witcher 2, were for the better. You spend too much time on going from place to place searching for people that may or may not be there, depending on the time of the day. This is made worse by the fact that there is no easy way to pass time on most parts of the game. Combat system is far too simple for such a long game, and it provides most challenge in the beginning and ends being very easy in the end when Geralt is all level up.
Despite the its flaws, I whole sincerely recommended this dialogue heavy, time consuming dive into the world of the White Wolf.