Short and sweet additional rules with an eye on the Princes of the Apocalypse campaign's themes. However, this product is now comprehensively redundant: if you want the extra PC races, they're in Monsters of the Multiverse, if you want the extra spells they're in Xanathar's Book of Everything, and that's pretty much all it has to offer. Full review: https://refereeingandreflection.wordpress.com/2015/11/19/5e-learning-to-expand/