Kids won't want to read it if they don't have to
I read this as an assignment for English, believe you/me I wouldn't have read this on my own. But I'm glad I did, this book is basically the foundation for all the pirate-hunting-for-treasure scenarios you see so much in TV, movies, books, etc. It drags during the "My Sea Adventure" section enormously, and the language is all pirate-y, surprisingly no swear words. I recommend it.
What other families should know
Too much violence
Too much drinking/drugs/smoking