Never read childhood favorites as an adult if you don't want them to lose their favorite status. The book is about 2 teenage twin boys who accidentally touch their father's science project and end up time traveling to a few months before the Great Flood with Noah and company. This was apparently very interesting when I was 12, but not now.
I found the author to be very repetitive. Just how many times can new characters discover that Sandy and Dennys are twins and be confused over it? Just how long does it take a real person to get over a bad sunburn? I've had such a thing many times, and it does not incapacitate a person for weeks. I also found the book to be too fantastical for my adult tastes. I had no desire to read about good and bad angels that transformed themselves into good and bad animals. I also found that there was very little character development except to establish who was good and who was bad.
The story was very different than I remembered it to be. I think it's probably a book best appreciated by pre-teens and teens rather than adults.