It introduced the basic technique and standard approach in modern macroeconomics, including linear difference equations, intertemporal optimization, representative agents and OG models, competitive equilibrium and welfare theorem, standard models of money (CIA and money in utility function), etc. It is good to think macroeconomics as a branch of applied general equilibrium.
It also includes some frontiers of research like RBC and calibration, increasing returns, multi-sector models, etc.
As it's name suggests, it tells much on multiple equilibria and sunspots, it maybe an alternative approach to explain the real phenomena.
The most important, all these materials are introduced in a moderate level. The mathematics used is more acceptable to the first-year graduate students in economics compare to some other texts.
Since it emphasizes on fluctuations, it lacks of some important topics like unemployment, labor market, incomplete and imperfect market, fiscal policy, policy-making, and little on endogenous growth. But it is not so bad, this keeps the text short and more friendly. Not a book can include all the important topics in the subject. The basic has been told, and all the others could upon to others.
So it is suitable for first-year graduate students in economics and is better to be used together with Blanchard & Fisher's "Lectures on macroeconomcs".