I was one of the reviewers of the book and I really liked the content. The book covers many different areas of APEX and combines it with other knowledge (SQL, BI, ...). Although most focus is on reporting (Classic, Interactive Reports, Charts, PDF printing, ...) and getting most out of that, it also covers the history and architecture of APEX, the integration with other platforms (OBIEE, webservices) and some options to improve performance.
You find more info about the book on the Packt website.