when I first heard the premise of The 13th Warrior, I thought here was yet another dumb arse film...
but dang if it wasn't a lot of fun and I rewatch it regularly. I even went so far as to track down a copy of Crichton's Eaters of the Dead to see how it was. The film beats the book hands down for me... but both are fine. The CGG of the storm was lame, but the characters were such fun I forgave them.

The early Harry Potter films worked because the themes were simpler.   But the later books were not really good candidates for film and each successive film just seemed to miss the mark more & more.

AS for Tolkien... what got published in the books was a mere fraction of the world he created, so I'm not going throw stones at Jackson for cramming as much as he did.... LOL