There are basically five types of cliffhanger-ish endings I can think of. Here they are:
Type A: At least one main character is in a truly dire predicament and wham! The book ends. This is like The Silent Tower by Barbara Hambly, which is still the worst cliffhanger ending I have ever seen in a fantasy novel. In response to Elaine’s comment, I think I’d tend to put Frodo’s predicament here, and note that it took at least a decade for me to read the whole LotR trilogy rather than skipping forward to pick up Frodo and Sam’s plotline in the next book.
Type B: All the important characters are in an okay place and there is a natural pause in the action, but none of the big plot threads have been resolved.
Type C: The Big Bad is ascendant plus at least one important character is in a fairly dire predicament when the story ends. This is like Jinx by Sage Blackwood. Also perhaps like the 4th book of Django Wexler’s Shadow Campaigns series.
Type D: All the biggest stuff has been resolved, but nevertheless, an important character has been left in a predicament of some kind when the story ends.
Type E: All the biggest stuff has been resolved, but there is at least one important plot thread that has been left hanging.
Vote, please! Which of the above types are really disturbing to you as a reader? Which, if any, are okay?