I lead a book club at my local library, and we've found the trick is balancing broad appeal with just enough depth to spark conversation. 'The Long Way to a Small, Angry Planet' by Becky Chambers is practically our club's mascot now. It's a cozy, character-driven space opera with low stakes, which is a relief for folks tired of grimdark. The found-family dynamics gave us tons to talk about, from how the crew interacted to the quiet worldbuilding that posed ethical questions without beating you over the head. We spent a whole meeting just discussing the different cultures on the ship.
For fantasy, Naomi Novik's 'Uprooted' worked beautifully. It has a fairy-tale feel that's instantly accessible, but the relationship between Agnieszka and the Dragon is prickly and complex enough to generate debate. Someone always brings up how the magic system feels organic. We've tried denser stuff like 'The Fifth Season' later on, but starting with these made everyone feel included, not intimidated.