Disclaimer: I know and like the author.
Just in time for the DSM-V (ETA 2013) Rich McNally presents an erudite analysis of issues of definition and classification of mental illness. The level of scholarship is very high as he takes on Wakefield's harmful dysfunction analysis of mental disorder, the question of whether personality disorders should be rated dimensionally rather than categorically, whether molecular genetics research is shedding light on subtyping of schizophrenia, how cultures shape expression of pathology, why mental illnesses have not diminished in prevalence via natural selection, and much more.
The writing and thinking are clear, but this is not an entry-level book IMO. Unless you can (and care to) keep straight social causation vs. social construction, adaptation vs. exaptation, pathoplastic vs. pathogenic effects, etc., it may be slow going at times.