You say it's a great book, yet you dismiss the very aspects that make it a great book. That in itself feels like a cop out, no offense.

As others have already said: it's a book about the zeitgeist in Europe prior to WW1. And it's set in a sanatorium of all places. I've always taken the slow pacing and the mundaneness of the novel to be an essential part of the narrative. You are meant to be bored, and you're meant to feel like you're losing your mind reading it. It's a hard read for sure, but by design.