Two of the four of us who saw the movie had read the book. All four of us absolutely loved the movie. It did not follow the book as well as I would have preferred but the changes made sense for the time and audience of the movie. Pierce Brosnan and Uma Thurman are fantastic. The casting of Percy, Anabeth, and Grover fits the characters very well once you change the characters from middle school to late high school.
Best statement I can make: none of us thought we were in the theater for 2 hours since we were so engrossed in the story.