I learned a lot by reading this book. It helps to understand central developments in the discussion of free will and moral responsibility during the last 50 years or so with a shift away from leeway freedom (i.e. the claim that in order to be free, the agent needs to have the ability to do otherwise) to issues of sourcehood (i.e. the claim that what matters is that the agent is the source of the action). I especially liked the extended discussion of Frankfurt's attack on PAP and the various ways of responding to his argument. At times, it seemed that Timpe spent too much time discussing specific papers that are not that relevant for the overall discussion, while at other times not being critical enough towards arguments that favor his own position, a form of source incompatibilism (see e.g. his discussion of Pereboom's 4-case argument which he endorses a bit too quickly). Compared with other introductions to the literature on free will, the book by McKenna & Pereboom covers more ground and is more fair-minded as the authors mostly abstain from arguing for their own views (see e.g. the much better and more thorough discussion of Pereboom's argument). At the same time, the book can be overwhelming and raise too many issues if the interest is to get a feeling for the overall dialectic. So both McKenna/Pereboom and Timpe offer good introductions but serve somewhat different purposes.
I found this book very clear and engaging. Timpe provides an overview in key debates on free will, including especially Frankfurt counterexamples that attempt to show there can be freedom even without alternative possibilities. Timpe agrees that the actual sequence of events is essential for freedom--he believes that the agent has to be the indeterministic source of her actions--but he thinks also that being the source entails some robust, morally relevant alternative possibilities. There are flickers of freedom insofar as, though one may have to do a certain action, the mode in which one acts can be different. I agree with Timpe's source incompatibilism but there needs to be more work on how this is metaphysically possible. Timpe needs to integrate his definition of free will with an adjudication of metaphysics involving substances or events, which he touches on early in the book. But the debate over agent and event-causation never gets a central place.