Apropos. I just ran a quick search on critical studies of Ken Wilber’s work. This monograph contains a whole chapter on ‘Integral or Muscular Spirituality?’:

Gelfer, Joseph. Numen, Old Men: Contemporary Masculine Spiritualities and the Problem of Patriarchy. London: Equinox Publishers, 2009. (224 p., ISBN 9781845534189) [Author website]

Chapter five features: An Introduction to Wilber’s Integral Theory — Ken Wilber and the Problem of Masculine and Feminine — Ken Wilber and the Problem of Patriarchy — Wilber’s Masculinist Style — Wilber’s Muscular Spirituality — A Further Take on Wilberian Masculinism (p. 143-180).

And there are also two articles dedicated to a critical review of Wilber’s work:

1) Brys, Zoltan, and Petra Bokor. “Evaluation of Ken Wilber’s Integral Psychology From a Scientific Perspective.” Journal of Spirituality in Mental Health 15. 1 (2013): 19-33. DOI: 10.1080/19349637.2012.737685 [Link]

Abstract: “Ken Wilber’s integral psychology (WIP) is a combination of a coherent spiritual philosophy and an abstract psychological theory. WIP sets development as a key element and it aims to synthesize a wide range of ethical, epistemological, and philosophical approaches as well as psychological theories and traditions.

The authors distinguish metatheoretical and theoretical parts of WIP, and suggest that the theoretical part of WIP is implicitly individual, neglecting important notions of social psychology. Further, it is claimed that spiral dynamics, a core element of WIP, contains idealistic, arbitrary, and moralizing categories, which in turn imposes a strong limitation over the whole work and confines it to remain a closed system.

WIP in general lacks the methods for validation and/or falsification failing, therefore to fulfill the criteria of scientific theories and the ground for scientific research. Yet by identifying the central elements of various abstract psychological theories in a coherent system and by offering a coherent categorization, the authors believe that WIP may deliver value to epistemology, sociology of science, and spiritual philosophy.”

2) Saitera, Sean M. “Universal Integralism: Ken Wilber’s Integral Method in Context.” The Humanistic Psychologist 37.4 (2009): 307-325. DOI:     10.1080/08873260903113550. [Link]

Abstract: “This article is an inquiry into Ken Wilber’s integral epistemology as applied to social systems, namely, through organizations and leadership.

It explicates the constructionist component inherent in the universalist nature of AQAL theory (a framework covering all quadrants, all levels, all lines, all states, all types). The relationship between integral methodological pluralism and the AQAL model are explored in the context of a fundamental misunderstanding of phenomenology, transpersonal psychology, and the human sciences, not as a method among many but as an essential characteristic of Wilber’s integral theory.

This article aims to contribute to the further development of integral research and design methods through clarification and contextualization.”

See also the Wikipedia article on Ken Wilber, especially the sections “Reception ” and “Books About Wilber.”