Following the Story
If you follow the book too closely that makes the game far too linear. You could have your missions based on events that occur in the book but don’t make the game revolve around the book. If you do want to follow the story because it’s a great story, then there are a few ways to go about that:
Character Growth
If your book starts off with a powerless character, I would start there. By allowing the player to grow and develop with the character in the book, then you’re allowing them to get attached to the main character. By doing this they will get emotionally involved and love the story even more.
Epic Battles
If the book has a war in it, take them there. Whatever part the main character plays in the battle make your player have that part. Let them wander through the battlefields clashing swords or gunfire.
Allow For Change
If you were to follow the story precisely as it is in the book, it might not be as exciting for someone who’s read the book and knows exactly what’s going to happen at each step of the way.
In order for there to be excitement for everyone you should allow for course-altering actions to take place. I would recommend talking to the author about this as he/she might have had something else in mind that their not using anymore, that could make for some great alternatives that greatly impact the outcome of the story.
The World
If you love the fantasy world and think that the story that’s been told there is great, but you want to do something original with that world, then I think that it can be done. If you implement all of the great things about the world then there’s nothing stopping you. Add in content that the book maybe missed or maybe the story takes place between books or before the series even begins. Most fantasy series have elaborate details about the world the books take place in and a history that already exists. Use that stuff to propel your work into greatness, assuming the author is on board.
The Character
If there’s a particularly entertaining or powerful character in the world, use it. Whether it be a bad guy or a good guy, tell their story. CD Projekt RED has done that with Geralt of Rivea and it has turned out very well for them. With the upcoming The Witcher 3, it looks as though they’re going to expand on his story even more. If you can find a character who is compelling and has interesting history, that adds for some great gameplay that you can put in, be it flashbacks, or them becoming powerful or emotional.
Final Words
I just think that books are a great starting point for video games. It allows for more freedom than if they were turned into movies because books take hours to read and video games take hours to beat. I think more authors should look into making their masterpieces into video games to allow more people to see what they’ve come up with, and possibly even get more sales for their books.
