Dune 3 ended in a weird and not so pleasing way (not that every book must have a happy ending, but eh), Dune 4 is starting in a super weird and even less pleasing way*.
Read the first one. Maybe the second. I'm going to keep going because that's what I do. You don't have to.
*It feels a bit like Austin Powers 2, where Vanessa turns out to have been a fembot and the happy ending is upended. I mean... It's nothing like that. But my feels are like that. For some reason.
tl;dr: Dune is weird.