"Wizards Presents: Worlds and Monsters" managed to be one of the most enjoyable Wizards products I've read in years. The goal of the book moves beyond merely presenting changes in cosmology and combatants as they transition from 3.5 to 4e. Most importantly, the contributors, all of whom are helping to shape D&D 4e, have shared their reasons for these changes, and explicate why this should help improve the gaming experience for players and GMs. (In fact, it would be nice to see this insider's perspective in other gaming products.) The contributors seem genuinely excited about the results of their efforts to streamline game play, make monsters more interesting (and less time-consuming to stat up), and create a new space for the D&D gaming community.
Why 3 stars, then? Because while the artwork is lovely and the prose seems serves well to generate interest, I do feel that the contents of this volume could have either appeared for free on the Wizards of the Coast website, or could have been bundled with the previous book, "Wizards Presents: Races and Classes" for a far less ridiculous price.
Be that as it may, I can honestly say that, after reading this book, I am as excited about 4e now as I was about that red box Basic D&D game I bought with my allowance money when I was 10, and THAT hasn't happened in a long time.