Thomas Brown’s objection to transcendental idealism (as he understands it, based on Villers): it is too realist.

In the mere belief of the subjectivity of perception, [Kant] is certainly not original; for it would be difficult to find a philosopher of the present age, who retains the belief of the actual unmodified representation, by the senses, of the qualities of external matter. In one circumstance, however, we differ from the transcendentalist. We own the subjectivity of our perceptions; but we are convinced of the impossibility of analyzing them into objective and subjective elements; since to us, by the laws of our nature, these elements must ever co-exist.” (“Villers, Philosophie de Kant,” Edinburgh Review 1 (1802–3):253–280, p. 265)