The Wellworld series (fantasy) by Jack L. Chalker back in the 1980s. I still have them but little desire to revisit them as so much else that needs reading.

The only other series that has taken me is the Millennium Trilogy by Stieg Larsson, which had me losing sleep to read. Had he lived, I would have followed the series as long as it lasted.

Unfortunately, I have been encountering more and more people that keep it for its influencing aspects. Thoughtful folk, I suspect, give it a 4-star rating and consider how to best use its stories.

Just to be different (and maybe controversial) How to Win Friends and Influence People, by Dale Carnegie.

It is praised by people hot on Social Engineering and two kinds of people praise it. Those who want to selfishly use its tools for their own ends and those who think it is actually high ethics, and will later challenge this belief.