There are, as of late 2008, nearly 900 UNESCO World Heritage Sites. This book contains 832 rather small pages, including multiple indexes, maps, and introductions. Which should tell you the biggest issue with the book -- there isn't nearly enough room to do justice to the subject.
For each site we get a heading (name, location, reason for designation, and a small map), and a brief-to-very-brief summary of the history of the area and why it deserves UNESCO protection. Most of the sites also get a picture ... very rarely two.
Most sites get a single page, a few get two pages, and quite a number get only half a page. The half-page write-ups usually lack even a single picture.
Now... one could argue that the 2-page sites ARE most worthy of the most attention; they are, after all, by and large the most important.
But one could also argue that these are the sites with which readers are ALREADY most familiar. Raise your hand if you have never seen a picture of (or visited) Stonehenge. Great Wall of China. Taj Mahal. Petra. The Grand Canyon. Uluru/Ayers Rock. Pyramids of Giza. The Acropolis.
Now raise your hand if you have EVER seen a picture of (or have even heard of or can name the country...) Royal Palaces of Abomey. Skocjan Caves. Dja Faunal Reserve. Lord Howe Island. Zamosc. Joya de Coren. The Rock Carvings of Tanum. As you've probably guessed, none of these latter group get a picture, or more than the briefest of write-ups.
This topic really deserves a far larger and more detailed book -- at minimum a large format 'coffee table' hard-back, or at best, a multi-volume set. Failing that, the UNESCO website contains a list of all their sites, with more pictures and at least as much description and links to other websites.