Vapid characters aren’t a problem if they are doing something interesting or if there is non-trivial conflict or mystery or confusion or tension or drama of any sort or anything that leads to some kind of meaningful change in a character. Gatsby's death might have counted if Fitzgerald hadn't telegraphed it from so far away that it became a non-event.

You know how kids’ books for beginning readers are mostly about stringing together words that are easy to read and make a sensible sentence? See Jane run. Run, Jane, run! why is Jane running? Because she wants to. That’s how Gatsby read to me with more complex words and sentences.

I don’t even mind books where nothing much happens (Iyashikei) if the setting is novel. But Gatsby was predictable and dull for me with cardboard characters living passive lives.

The other book that lots of people seem to love that I've never been able to finish is Moby Dick. I don't dislike it but he pace is a bit slow for me.