This book serves as a great introduction. I intend to give it to my children (when I have them) and this book is certainly geared towards kids/teenagers.... yet there are times when the language of the book is complex and grown-up, too. It won't talk down to your children, which I like, and there is a lot of text here.
My favorite feature about the book is the layout-- some pages will bring together myths from all over the world on one page. For example, in a page about the "underworld" or "creation myths" you aren't just getting one or two, and not just the usual myths, but a wide variety of myths from around the world, all on one page. This makes for an easy comparison, and makes the mythology and legends seem much more universal. Yes, there is a good chunk of time spent on the Greek Gods, but many many other cultures are represented here too, which I love. I haven't seen many mythology books that were so good at bringing together so many different cultures and different mythologies.
The book doesn't go very far in depth at any time. For adults, this is an easy resource, a quick overview, something to give you ideas of things to look up or explore further (if you're interested in learning about mythology). It's great at showing the places where myths, even from far away, can be similar.
There are some small things that don't seem quite accurate, and as I said, this is really just skimming the surface of a lot, but for something to get your kids interested or to just start learning about mythology, this is a great great beginner book.
Most of the visuals are great too. Occasionally they seem out of place, but most are very good.
All in all, as a place to start, I highly recommend it!