Those of you who have read House of Leaves probably agree with me that in terms of the structure of the book, it's certainly creative. I want to say more but don't want to take away from the experience for people who have not read the book. I'm in the middle of this thing but definitely made me go wow, I've never ready anything like it before.
But that's not the only type of creativity I'm talking about either. I mean the creative aspect may be just about the story or the world where the action takes place. Or the drawings or figures used may be quite original, for instance.
Of course, the book could even be nonfiction (e.g., instructional). In fact, those are the books I often enjoy the most because reality limits your creativity, so you have to really come up with something new yet factually true, like the relationship between math and music or art and science more generally, to be considered inventive.
Let me end with one last example: I never read Ulysses but watching a video about how Joyce planned and layered the book was astonishing. There are so many reference and symbols, I think the book must be considered a unique work of art that has little competition in that sense.