The 'Jurassic Park' book is much better than the film, it makes much more sense -- the reason the mathematician going is explained -- though I do like Jeff Goldblum's version better.
There was other things left out, like the Dinos that escaped on their way to the island.
As for the sequels, they are just silly!
I've read a lot of Michael Crichton's books, and he must write them with a film in mind, they are always so vivid, you can just see a film producer/ director reading it and immediately wanting to make it.