Not GP, but I think I made it to about 20 pages into the third book before giving up. I actually enjoyed the first book, but it just got more ponderous as it went on. And this was around the same time I read the Foundation series by Asimov, so I didn't necessarily need at pot-boiler.
I'm not sure if one of us misunderstood "pot-boiler" but Dune is surely no popcorn entertainment. It felt ponderous because its author invests much time into the development of characters, philosophy and politics. It's not for everybody, but it surely is not a pot-boiler.