My off-the-cuff critique of cultural studies would be:
Cultural studies wants to be given credit for being anti-elitist. Elitism is foul, but a cheap anti-elitism can be even worse, especially when hegemonic political forces no longer have much use for high culture. Cultural studies often has an uneasy relation to its objects of study. It doesn't really value them, all that much, in many cases. Its arguments for them are that they aren't elite, that they are popular (in two senses: appealing to a lot of people and in some sense belonging to the "people"), and that they do political work of a useful kind. The hermeneutic model for interpreting popular or mass culture is often very weak, based on unexamined ideas about "anxiety." Its politics focus too much on whatever immediate problem is besetting the culture, and so much of the work gets out of date rather quickly. Finally, it is literary in a way that it doesn't always recognize, relying on romantic narratives.
That's how it seems to me. There are a couple of caveats though. My critique of a lot of literary studies would be equally harsh. Any given article in cultural studies is as likely to be brilliant as in any other field, and it is unfair to hold different standards for different fields. 90% of everything might be crap, after all.