What is an example of an adaptation of a book where the TV series was better?

I'm bending the premise a little bit: The Boys is based on a graphic novel and bears almost no resemblance to the source material. I think the show is way more compelling and engaging than the graphic novel, probably because the show is written to be aggressively topical, while the graphic novel concluded over a decade ago.
- Also I've heard that the comic is gruesome, gratuitous, and horrifying just for the sake of it.
  
  Yeah, the author, Garth Ennis, seems to be pretty polarizing in comic book fandom based on what I read on Reddit over the years. I haven't actually read any of his work but from what I gather, being edgy the sake of being edgy is his thing.
  Another series based on one of his books that people say is better than the source material is Preacher.

I'm not sure about "better" but I would point to the IT and the Stand miniseries from the 90s that were excellent. Both books had parts that were problematic to put on screen, and a lot of fans felt the omissions were improvements. Also, the author was heavily involved in the productions, writing the scripts and consulting with the directors.
I don't think they make tv shows out of bad books, though, so I'm having a hard time thinking of other examples.
- Similar with The Expanse. There isn't a huge difference, but changes were largely for the better. The authors of the books also wrote the show, so they could polish things while adapting it and know where things were going in the future.
  I really hope that the adaptation comes back for the rest of the books at some point. In the final season, they included a short story in the show that occurs at the same time, but is only there to set up the last arc of the series. I didn't get why it was there in the show until I read the later books.

Do comics count? The Walking Dead because it was way different and more creative. But I still like the comics.

The Fall of the House of Usher not only improves the original story, but beings many of Poe's works to life in a cohesive, beautiful way.
I'm also much more a fan of Flanagan's Haunting of Hill House than Shirley Jackson's, but I understand that's a controversial opinion about a widely loved book.

Altered Carbon.
- The first season was phenomenal
  
  Yeah, but I didn’t like the character change they did in the series, simply because it wasn’t necessary. Nothing would’ve changed if they just followed the book, because it’s pretty straightforward and should work as a straight-up adaptation.