For example, pretty much everything by Michener is amazing, but nobody cares about him any more. He's dismissed as some kind of trashy or middlebrow post WW-2 writer; maybe he was -but he's also almost always a lot of fun to read, and occasionally incredibly interesting.
The Bjorndal Saga by Trygve Gulbranssen is largely forgotten in the US (maybe less so in Norway), but won all kinds of presidential awards and was a big deal in its day. It's sort of like "The Leopard" which is less forgotten, since they made a decent movie out of it (probably the great Italian novel). Greater novel though, in my opinion.
Another one I picked up because of an interview with Jim Simons; Jan de Hartog's "the Captain" -so far so good; was a big deal back in its day; it's predecessor "Captain Jan" was important enough it figured into Holland's war story. Totally forgotten now in the anglosphere anyway, and I'd have never heard of it if it weren't for a one off statement by an important guy who could hardly remember the name himself.
Dennis Wheatley is another huge best seller from the Ian Fleming era of trash novels; loads of fun to read -vastly better than Fleming. Alas, the movies they made of his books were all "video nasties" rather than James Bond.
None of these are Nobel Prize in Literature tier books, they vary wildly in quality, but they're loads of fun to read now as they were back then. Books don't always need to be an exercise in self improvement.