Hard disagree. I felt Dune Messiah really concluded the story told in Dune. Children of Dune was pretty good, not as good as the first 2 though, but set up God Emperor which is fantastic. A lot of mixed feelings for Heretics and Chapter-House, but books 1-4 are great.

What’s the reason behind the disappointment?

Came here to see if anyone would mention Dune.

I absolutely loved the first part. I do actually like the other parts, but imo they're nothing like the first one.

I re-read Messiah and Children recently probably for the last time. I’ll certainly re-read Dune again. IMO, they aren’t as good but it’s not as bad as some of the horrible sequels mentioned here. Ready Player Two tops my list.