A great RPG

Epic storyline and extremely well written with a gripping storyline that keeps us in suspense until the end.
A world where Manichaeism is rarely the standard (so rare in video games) or not everything is black or white, everything is a matter of perspective.
Choices that are radically changing adventure and they are really many (as you say that the re-playability is great!)
A soundtrack divine.
A rich cast of characters and very well built, each with a detailed background.
A main characters in class (for the heroic fantasy has its yes!).
A world of dark fantasy really dark in neat atmosphere as well as audio visual, teeming with life.
Many side quests which quite not content to be stupid monsters hunting or gathering RPG as numbers but actually helping the player to immerse themselves in the game world.
A thorough and comprehensive gameplay that requires an adjustment period, especially as the game is necessary (normal difficulty) but at the time of the games even more simplified or you press a button and everything is done alone this is far from being a defect and grows to truly master the gameplay.

In short if you are looking for a great adventure in the exciting story in a fantasy world worked given a chance to The Witcher 2.