Given reviews from Amazon, classify those review based on their content into two classes: Negative or Positive.

Let me give you an example: I've read this book with much expectation, it was very boring all through out the book
The answer to this example can be: Negative
Here is why: Review writer does not like the book because it was boring, therefore it is a negative review.

OK. solve this:
The book gives practical advice for those with diabetes. I've had type 2 diabetes for 13 years and when another ailment required me to use prednisone, I needed insulin. Dr. Bernstein's book taught me about the types of insulin and syringes. His book removed my apprehension about needles and possible low blood glucose. Like many pioneers in medicine, Dr. Bernstein's ideas were opposite to mainstream methods when his book was first introduced. However, his recommendation for a limited carbohydrate diet like that of the late Dr. Atkins, appears to be gaining acceptance. Control of diabetes is very much up to the patient. Dr. Bernstein's book puts life-saving knowledge in the hands of the patient. I have found it invaluable.
Answer:
Positive