3 things comes to mind:

1) After seeing Tales from Earthsea by Mihazaki's son, I started to read the full saga and... I was surprised. A lot. Especially because Sparrowhawk is the protagonist and not the Gandalf like mentor? And... it starts a lot BEFORE the movie, even if the movie say that they adapt the first 4 books?

I loved the strange world of Earthsea in the books. It was SO different, and evocative... I loved the atmosphere of the tomb of Artuan.

The movie is a strange disconnected mess of abandoned plot points that leave you with a lot of "maybe this was cut for time reason" and actually... are only "there" to be there.



2) Avatar - the last airbender

I've seen the M.Shyamalan movie before... and I liked it. It wasn't "good" but it wasn't that bad. (also, the DUB solved some tonal problem compared to the english version)

And I decided to get the cartoon. I remember coming here to see If I could skip the first book and go to the second (I wanted to know who was that girl put as a sequel bait! )
I red the hate for the movie.

I was a lot "why?"

Then I viewed the Legend of Aang.

And I understood. I understood SO MUCH.


Interesting note: as an experiment, I did the same thing to a friend of mine and my brother. Same result.

3) Shinobi: Heart Under Blade

Never read the original novel, but after this I red the manga Basilisk and... it was VERY different.
I was under the impression that the movie was based on the manga (that was what my friend who suggested it told me), but now I find that they are both adaptation of a third media... so, let's simply say that they are VERY different.

Even the titular Basilisk is a different person between movie and anime/manga. Also, the manga/anime ending is very romance tragedy, and I love it so much.