classifying entertainment

Is there defining criteria for a good book? Or is this left up entirely to the individual? Is there a difference between the standard “good” and a person’s preference when it comes to entertainment? For instance, is it fine for me to claim something is a good book, or must I say “I think it is a good book”? I come to this question because I was wondering what exactly it is that I think about the book I just finished reading last night, The DaVinci Code.
Yes, it is written well.
Yes, it is very entertaining.
Yes, I had a hard time putting it down each night.
However, I felt a little messed up by it while reading. Now that I’m done (and no longer immersed in the book) I am fully aware that it is a fiction novel. The problem lies where the book makes reference to so many things that really exist. Therefore, the mind starts to wonder if these fiction characters are really onto something. I found myself contemplating whether some of the bizarre ideas about Jesus and Mary Magdalene presented could be true. This is what makes me think maybe it’s not such a great book.
Any thoughts on this?
I also strongly desire a trip to Europe after this. I’ve never been. Anyone up for it?

Last night, some friends and I ventured down to the Brew & View. (For those unaware, this is a movie theater/bar where one pays $5 to get in and then watches 2 movies.) The double header last night was first Anchorman and then Dodgeball. Many laughs. he he ha ha ho ho.
I suppose my final thought on this topic for now is that we must categorize movies and books. These movies definitely accomplish what was intended, mindless laughter. So in a sense, that makes them "good."