It's important that it can stand alone and still leave room for a sequel. I think the difference between a true cliffhanger ending and a satisfying ending to a stand alone novel is that in a cliffhanger ending, the main story or question is not finished or answered in the book and you have to read another book to find out what happens (for instance, a murder mystery where you don't find out who the killer is until book 2 - have read a series like that and was so frustrated that I stopped reading right after I found out who the killer was in the 2nd book - I didn't trust the author not to leave the reader hanging again at the end of the 2nd/3rd etc. books).
With a standalone novel, the questions are answered, but there's a hint at the next adventure or a few loose ends that lead into the next book. For instance, in a murder mystery, the killer would be revealed and maybe even caught in the first book. At the end of the book, there could be a hint that maybe he escaped, or the main characters have another murder to solve, etc.