Series You Have Started, but Not Yet Finished

I know that some series are hard to get into. Others just seem to go on forever and I lose interest. Here are 100 series (and yes, there could have been many more) for your consideration. These are not all series that I have put down, but I know folks who have not finished each of them. There are books aimed at children, juveniles, YAs and adults. All but one are fantasy or science fiction. Feel free to comment with other series you wish had been here!