I am a longtime fan of Ann M. Martin, and I consider Rain Reign one of her best books. Martin's writing is clear and concise, and her characters are vivid, realistic, and relatable. Autism is a topic that is close to Martin's heart, and she writes about it with sensitivity and a great deal of background knowledge.
This book is often compared to Mark Haddon's The Curious Incident of the Dog in the Night-Time. I find Martin's book superior to Haddon's in many ways: it is better researched, more realistic, and more enjoyable.