I was honestly not expecting much from this product -- the basic idea, showing dungeon crawling as a professional sport, is cute but could be fully explored in a much smaller, cheaper book. Just adding the higher level spells to the d20 Modern rulebook would be able to handle it.
I was very pleasantly surprised. There are a couple of (useless) prestige classes, a rather silly system for generating a "nested" GM within the game, and some good new items and spells. Surprisingly, though, the meat of the book is a full-fledged setting, a differently-imagined dystopian America ruled by Emperor Ronald Reagan and dominated by clergy of the Roman Gods.
Xcrawl itself isn't the most interesting feature of the setting, but it's a great excuse for getting PCs up to a decent level before involving them in the real meat of the setting -- the intrigue in the Leagues, how they can use their celebrity to change the world around them, and how they interact with the lunatic populace and government.
The oversimplicity of the idea they're selling the book on should be chalked up to the marketers. The writers and designers did a crackerjack job creating an innovative "fantasy modern America" well worth exploring.