Between the Pages is the place to go to for more general discussions/debates that could be perhaps be inspired by a particular book, but could extend beyond it and are applicable to a wider range of books, or even a particular genre.
For example, “What do you think of a series of books that introduce a wide range of characters’ perspectives and/or time frames?” Wheel of Time books (Robert Jordan and Brandon Sanderson) is one example of a series like this or the Emelan books (Tamora Pierce). There are several other series where this could be applicable.
Or you could flip it around and ask "What do you think of a series of books based on stories which are mainly told from one person's perspective?" Such series could include the Harry Potter books (J.K. Rowling) and the Dresden Files (Jim Butcher).
Another discussion could be of plot devices and/or story arcs, such as the Hero’s Journey, outlined by Joseph Campbell
What about a topic about the effectiveness of multi-part series/worlds eg. Heralds of Valdemar and Realm of the Elderlings?
So many books and series to compare and discuss!