Paris, Chatelet Les Halles
Almost the entire city is within 20-30 min on transit from the RER B axis. But based on your characterization of Châtelet as a "god forsaken hole in the ground" (on est laïc ici, merci, which makes pretty much the whole of the hexagone "god forsaken"), perhaps you should head out to one of the fancy restaurants near l'Etoile, or go have a nice little meal inside the Galleries Lafeyette. Or go buy a good sandwich on your way in, and enjoy the intersection of the two Frances at the Forum des Halles.
My initial reaction was sort of similar to yours. And then I realized that I didn't really know what the OP meant by godforsaken... because it is a huge and confusing transit center to those unfamiliar with it, because the food markets of Les Halles were so different from the mall that is there now, other reasons...?
A lot of locals do not like the redevelopment that was done to Chatelet, Les Halles, hence my question about what the OP was looking for, and offering the possibilities of other easy to reach locations.
The RER makes several stops from CDG (I assume this is the airport you mean) and in Paris. Some trains have fewer stops than others, but all make stops. And of course, you could hop on a connecting metro as well and widen your options even further.
What time of day will you be there and what kind of food and price range would be ideal?
(Edited to add) If you haven't seen this thread, I think it has useful info for you: