I have always been a Star Trek fan and was eager for the new movie. Without giving away any of the plot, I must say I was impressed with what the writers were able to accomplish. They have re-imagined the series in a manner that will attract and delight new fans without ruining the story for the older fans. The original series and subsequent movies and spin-off series remain intact, and that was no easy feat!
Consider the fate of most book-to-movie adaptations. The book is always better than the movie (unless it was written second) and usually the movie is a BIG disappointment for the fans. Part of this comes from condensing a large novel into two hours of movie. A lot comes from the fact that fans form their own ideas of what characters and scenes will look like, and rarely does that vision match what is on the screen. And some comes from writers & directors who simply do not understand the spirit or message of the book.
Sometimes it works. The Lord of the Ring movies were incredible adaptations, in part because director Peter Jackson's such a huge fan of the books.
Sometimes it's almost scary spot-on, such as with The Watchmen, which was almost frame for frame identical to the graphic novel.
More often than not, the movie falls short and misses the mark by miles. One of the worst adaptations I've ever seen was for "Flowers in the Attic."
What's the best and worst adaptation you've ever seen?