The Witcher 2 is a sprawling RPG following the story of Geralt of Rivia, from the book of the same name by Andrzej Sapkowski. Geralt is a Witcher - a genetically altered human trained to fight monsters, and possessing special powers. It's one of the best role playing games ever made.
While based on a book, you have a great deal of freedom and there are numerous paths available and multiple endings. It's a challenging game right from the start, but perseverance in The Witcher 2 will really pay off. Combat is a steep learning curve, but the exploration and conversations you will have make up for this.
The world of The Witcher 2 is genuinely breathtaking. Beautifully designed, with a wonderful weather system, this game is enjoyable to just be in. The sound is similarly detailed and fits perfectly with the game. There's a lot to see in The Witcher 2, and some decisions have huge implications, meaning there is a lot of scope for replaying the game.
If you're looking for a single player fantasy role playing game - The Witcher 2 is a masterpiece. It may not be the most accessible, but once you are in its grip, it won't let go until the end.