When a book becomes popular, or at least has fans with money to spare, it’s likely that said book will inspire a television series or movie.
I’ve seen quite a few adaptations that were done well (most of the Harry Potter series, the Hunger Games), some that sucked (anyone remember Eragon and the way too many changes in the first Percy Jackson?) but were good if you didn’t compare them to their books. And then there’s the very few cases where I’ve (gasp!) found the movies to be better than the book.
(Now I’m not going to go into those too much because I know I’d just end up babbling and off topic but in both cases the movie was fun and funny while the books tried too hard and were full of long winded paragraphs of unnecessary back stories.)
What does work for me? When it comes to books with adventure, magic or post-apocalyptic settings I see the benefits of making a movie. Some things are hard too imagine. But, for me, the recent influx of sob story films based on more realistic books have fallen flat. The Fault in Our Stars and If I Stay? Definitely did not have to spend the time both reading and watching.
The most interesting thing about turning books into movies is the division between every one involved. Book readers vs. movie watchers. Readers who understand why changes were made and those who don’t. Scriptwriters and directors who try to honor the source material and those who clearly didn’t understand the significance of certain “scenes.” (I’m looking at you Harry Potter and the Deathly Hallows part two people…it was very important that Voldie die a “human” death and with an audience!)
One thing I will say. If I read the book first it’s pretty much a given that I’ll watch the movie, even if I didn’t like it. If I watch the movie first and don’t like it I’ll likely stay far away from the book. My “to read” pile is too big for that.