Wow, I'm a native English speaker, but this is pretty subtle. The easy answer is: There is no difference. You could use them interchangeably and no one would think anything of it. I suppose "Is it any good?" is less formal and less literate. You would ask this in an off-hand way, as if you really didn't care much about whether the book is worth reading or not, because you are not planning to read it anyway. On the other hand, "Is it good?" could go either way. It could be just a casual question for the sake of conversation, or it could be a sincere request to learn something about the qualities of the book. By the way, I haven't read The Idiot. Is it any good?