The books primarily succeed because they create a nuanced emotional world rather than a cohesive story which could be followed logically. As a narratives go, it's messy, much more like a series of short stories with gaps and jumps. This explains why the books were essentially unknown in the US prior to their adaptation into a video game. What it does have are excellent, flawed characters and an immersive world. This seems to have given the games a lot of leeway to pull narratives together, which they did very very well. That puts the show in a difficult position of attempting to honor both the books and the games, or rather the happy position of being able to pull material from both to design and satisfy the original narrative intent. And they did a fantastic job (at least for the first two seasons when this was written).