The actors were good. Dev Patel did a good job. I saw the "desipan" in him when he says "Arey Bhaiya, I am the dishwasher." Overall, he justified his character. Freida Pinto, the leading lady, was okay. I felt she was more of a pretty face than an acteress. She cannot act. I would like to see her upcoming works to see if she truly has the talent. The kid actors were excellent. They definitely deserve all the fame they got.
Comparison to the book: The book is much much much better. That is all I have to say. The movie is nothing like the book, as in quality and content. I think people should read the book.
The main character in the novel has no religion. His name is "Ram Mohammed Thomas." More about the book here.
Overall, I enjoyed the movie. However, I don't think it deserved all the Oscars it received. I did like the songs.