I find my Graduate theory students prefer to make an external critique to an internal one. In other words, they are interested in what a particular theorist does not mention. If a theorist does not mention something, they conclude that their theory does not "cover" what is omitted. That is the student's main criticism of the theoretical article. The students are especially hard on theorists for not predicting the future, failing to account for things that have not yet happened.
An internal critique would tease out the inner contradictions of an argument, its incoherences, the inherent weaknesses of its argument.
I am guilty of external critiques myself. It can be a convenient way of "clearing the ground." Absences do speak loudly. Yet I find them also too easy, a bit cheap, as it were. You don't really have to look very hard to find an error of omission.
The external critique I am most fond of is when critics assume that the novel is the only significant genre. Then it is easy to see what the introduction of essay, poetry, and theater does.