Don't worry - there are no spoilers here...
In short, it was a fantastic movie. The special effects were excellent, the story was a rollocking good romp, and the casting was great. The film is not identical to the book, but it is faithful enough, and most entertaining.
Most of the same old familiar characters were there, along with a few new ones. I thought Kenneth Branagh was great as Professor Lockheart (is that the right name?).
If you have read the book, you are sure to enjoy the film. And if you see the film, you will definitely want to read the book afterwards, to get all the extra detail and background about the story.
I give it 4.5 stars. (I'm saving the other 0.5 star for the next LOTR installment...!)