I too would give this movie only a half a star, if possible. As a Dan Brown fan, I expected a lot from this movie.
I can't even begin to describe how disappointing I found the movie. The C.E.R.N. angle was almost completely eliminated. The end of the movie was changed from the novel (and not for the better). There were key relationships that were changed or omitted (for unknown reasons).
The only piece of the movie that even came close to meeting my expectations was the explosion of the antimatter.
If you have read the book, I would NOT recommend the movie. If you have not read the book, I would recommend reading it instead.