Dvoretsky's book is for advanced players. In order to get maximum benefit one should probably have a rating of at least 2000 FIDE (app. 2100 USCF). At that level basic tactical skills would be in place. However, in order to develop further one must work with more complicated material, basically well-annotated complex tactical games. This is where Dvoretsky comes in. The book is packed with complex games and analysis of very high quality, with additional observations and succinct advice about decision-making and psychology in tactical situations. In this book chess is a very concrete game - the master-teacher is a firm believer in the power of the specific example more than in overall synthesis or general conclusions.