Malebranche was one of the finest minds of the last century: but unfortunately his imagination had too much sway over him. He saw only by its means, and believed he was hearing the responses of uncreated wisdom, of universal reason, of the Word. Granted, when he gets hold of the truth, no one can be compared to him. What sagacity in disentangling the errors of the senses, the imagination, the intellect and the heart! What touches when he paints the different characters of those who go astray in the search for truth! Did he go wrong? It is in a manner so seductive that he appears clear even in those passages where he was unintelligible.
This is from Condillac's Traité des Systèmes (1749), as quoted in Pyle's Malebranche, p. 259. It needs far more development than this to stick, but I think anyone who has done any extensive work with Malebranche will recognize that, yes, one can see how this might be a sustainable criticism. It's also an extremely clever and subtle ad hominem, since Malebranche devotes a considerable section of the Search after Truth to the errors of the imaginative people (he discusses Tertullian, Seneca, and Montaigne as examples), and it would be a delicious irony, even for those who, like myself, have an affection for the Oratorian, if he were to exhibit the same symptoms.