A good table of contents is basically a trustworthy promise between you and the book, right? I get so annoyed when I pick up a nonfiction title and the TOC is just ten chapters with super vague titles like 'The Beginning' or 'A New Way'. For any book aiming to teach or inform, I need to see the actual sections and sub-sections clearly listed, with page numbers that are accurate. Memoirs and novels can be a bit looser, sometimes just chapter numbers or titles, but even there, a clever chapter name can set a mood.
What I look for more and more, especially in ebooks and audiobooks, is a breakdown of parts. Like if a fantasy novel is split into 'Book One: The Shadow' and 'Book Two: The Light', that should be in the TOC ahead of the chapter list. It helps you gauge the structure. I've also seen some books include the page numbers for illustrations, maps, or the index in the contents, which is super handy if you're flipping back later. Without those details, I feel a bit lost before I even start.