Best interactive iPad books of 2011 for adults

Interactive books for kids hit the App Store every week, but mature readers have fewer options as most turn to iBooks and eBooks. But, that doesn’t mean a few gems that use digitization well without compromising content emerge every year. This sector is grossly under-reviewed and the offerings can be very pricey making it hard for readers to decide which book-apps are right for them. These are the best of the lot from 2011, which, if you read them all, should keep you busy well into the New Year.