Funny thing is, so far the first season was the worst for that, since many of the castaways have personal secrets which define them as the story progresses but take time to be exposed in the first place.
Maybe I’ll have egg on my face as I progress, but I definitely remember seasons 4 onward doing a better job of hinging suspense on story and conflict rather than “ohmygosh what was that?” and added complexities. It felt less like they were just throwing new pieces on the board (Nikki and Paolo, the second island) and more like they were shaking up what they already had. I think the show has a certain sweet spot where it knows exactly how much of it all is bullshit.
Funnily enough, I’m threading my Leftovers rewatch throughout, and definitely know what you mean: they let the mystery be, character supersedes plot, and every time you think they’ll wring tension out of contrived drama for episodes on end, they rip off the band aid and make hay with the consequences.