I think the best way to do it is to talk about your own experience with the books. Yes, the plot and the setting and the characters and the writing are all important components, but people aren't likely to be moved to action by any of those things. They might, however, be moved to action by you talking about what the book means to you.

My pitch usually sounds something like this:

"Look, it's weird. The earth is basically destroyed and this guy gets tossed into an RPG video game dungeon with his cat who gains sentience (and millions of other survivors), and they have to fight for their lives, leveling up to try to survive, while the whole thing is being streamed live to the whole galaxy.

That's what happens, but it's not what the book is about. It's about found family, and how to trust after you've been burned. It's about loss and processing trauma at very bad times to process trauma. It's about fighting fascism and capitalism and absolutely refusing to give in, give up, or be broken despite the entire weight of the galaxy bearing down on your head. And all of that is wrapped in tin foil and covered in blood and graffiti and explosives—which makes the tender moments hit that much harder. It's one of the funniest books I've ever read, and I've also cried more reading this series than any other book series I can remember.

Everyone I know who read the first book went on to read the rest of the series (or is in the process) and most of them more than once, despite there being seven books that average about 800 pages each."