Sci-fi and fantasy adaptation

In general, do you like the adaptations of sci-fi or fantasy books into films? The question is simple
There are a lot of good films, based on books. When I ask to someone who readed the book of a film before watching the film, he/she tells me in most cases that the film is a disaster.
What do you think about this? Can be a film at the height of a book? (not just on complexity, because the imagination is unlimited, but the money is not)
Ex. Harry Potter, Lord of the Rings, I robot, etc.

What do you think about it?

Hello everybody

Hello people on the web, this is my new blogg. I´m starting to think new things to post here, and in the meantime if anyone can help me with new ideas I´ll be very grateful.
I´m interested on the net, music, technology and the world of fiction.
I´ll be updating ;)