Star Wars, Lord of the Rings. Epics considered essential viewing that leave me cold. Game of Thrones was the same; the moment a dragon showed up I was checking out.
I've seen both Dune movies (the recent ones, not the camp Lynch adaptation featuring a oiled Sting) and I found them kind of dull, kind of silly, and very long. The inevitable third instalment is still going to be a tough choice: go, and complete the trilogy, or skip it and never think about it again.