Deneen's thesis is that the current malaise of liberalism is mainly due to inherent consequences of liberal ideas themselves. As these ideas and values have successively been influencing society, their unintended but necessary effects are the problems we face today: populism, alienation, commercialism, depletion of the environment, income inequality, etc. He makes the point that there is no easy way of fixing liberalism, since the causes of the problems are in the roots of liberalism itself. If there is one stylistic problem with the book, it is that he makes this point far too many times.
Although I think there is some merit to the argument that the current problems of liberalism are due to its fundamentals, Deneen does not seem to realize that his argument proves too much. He states that at least some liberal ideas stem from Christian thinking, but if that is the case, did not those original ideas also contain in themselves the same self-destructive potential that he attributes to liberalism? Is it perhaps so that those Christian thoughts also contained in themselves the seeds of secularism and of liberal developments? This is at any rate the thesis proposed by Larry Siedentop in his "Inventing the Individual", which I have reviewed briefly in this site. If Deneen had read Siedentop, he would have had a more difficult time portraying the emergence of liberalism as a fall from the communitarian Eden of previous times. Incidentally, it is hard to figure out when that Eden was supposed to have existed. Sometimes, Deneen seems to locate this Eden in the New England as described by Tocqueville, but at other times one gets the impression that he is talking about pre-renaissance times.
Towards the end of his book, Deneen does grudgingly accept that liberalism does represent some kind of advance. Although he is unable to say this without reiterating his withering contempt for liberalism, he is explicit that there can be no turning back. He has a very hard time proposing an alternative. He describes rather vaguely a so-called Benedictine option, a kind of low-key communitarian practical living that attempts to carve out a space outside of modern society. A community basing its life on organic tradition is to be achieved by explicit design. Deneen is conscious of the inherent contradiction of this proposal. So, the book is a failure, but an interesting one.