However, his book is entirely mum on the fact that there are different schools of thought, e.g., Keynesians, Classicals, Monetarists, Austrians, etc. A reader comes away thinking that all economists agree with Mankiw, and that simply is not true. Many other principles-level economics books have specific chapters devoted to these schools of thought.
In my Macro classes, I put Mankiw on "reserve" in the library and suggest that students read the 5 chapters dealing with "The Data of Macroeconomics" and "The Real Economy in the Long Run." However, I use other text books for the rest of the course, since they explain why economists disagree, give better information about actual public policy issues, and help a student understand, e.g., what the federal reserve is doing, or why some politicians like deficit spending and others dislike it, or whether the trade deficit is important or not.
For a reader who merely wants to understand the core issues mentioned above, Mankiw is a good book which I highly recommend. For a reader who wants to understand the nature of the public policy debates over these core issues, Mankiw is a horrible book which I suggest that you avoid like the plague.