The question at stake is something like: can a rational system be totalizing? And the critique is a theoretical argument that concludes that no, it can't. There are domains of the unintelligible.
The counter (from, for example, Habermas) is that the theoretical argument presupposed the very rational principles that are allegedly undermined.
In only the most uncharitable readings does this render the critical project completely impotent. For if the logic of the critical argument is sound, then it does in fact force an opening of the conception of rationality into something else; most likely something broader, perhaps more formal, and probably something that contains the previous conception of rationality as something like a special case--hence preserving the pedigree of the current perspective. The metanarrative remains, but in an evolved form. This is probably where Habermas is going, in shifting the locus of rationality away from the individual subject into the communicative realm. The individual talking rationally to himself remains as a
degenerate case.
But what if the critique cuts deeper; what if it simply scuttles the raft, or severs the chain between the earth and the sun. It might be that then, we are just completely fucked. Or maybe we can find a new foundation for validity. Maybe our own hot tongues can lick the salty ice of chaos into form.
For now I am dragged along with one foot dragging in the water; from this rapid vantage point I can examine the ecosystem that lives in the wake and foam. If there is a secret to life there, I want to know it.