Part of the exercise for the PRINCE2 2009 release was to shorten the previous 2005 manual from 457 pages to a slimmed down 327... This was accomplished by introducing two books, one for the PM practitioner, Managing Successful Projects with PRINCE2 2009 Edition Manual, and this one for the Project Executive, Project Board member or Project Sponsor.
If it is for guidance on how to be a Project Executive, Project Board member or Project Sponsor it is a reasonable book... though personally I think it could be shorter. The topic in and of itself is crucial, though I question the notion that a senior manager will read a 166 page manual... this is one of those areas where a half day or one day customized training course may be a better solution. There is no official OGC course at this time associated with this book which is unusual for the suite of OGC Best Practice Methodologies.
There are some other PRINCE2 "project management guides for sponsors" available that are quite good... for example the dated Prince2 for the Project Executive if still available. The Executive Guide to Directing Projects: within a PRINCE2 and MSP Environment (Prince 2 & Mcp Environment) is 124 pages and is an excellent in between option. The Prince2 Pocketbook along with clearly defined Roles and Responsibilities may be enough as well.