My two daughters (ages 2 and 4) request this book be read--at least once a day. It's a typical Dora the Explorer book with Boots. It has big words and colorful pictures. The stories are simple and not too long. I think it's probably geared toward the preschool/beginning grade school set.
Certain words have little "pictographs" with the word that it's for directly underneath it in smaller print. I suppose this is to help the child learn to read these certain words. Since my daughters are still pretty young (the oldest is now just learning the sounds different letters make; she already can recognize all the letters), we haven't really tried to use these little pictures in that way. Although, we've read this story so many times to them that they "read along" by reciting from memory certain parts of the story. All Dora the Explorer books are great fun for the kids because it involves them in the story much like the TV show does.
I highly recommend it.