After reading several reviews, I went to Catedral to see if it lived up to the hype. The person who joined me lived in Oaxaca for 5 years. I am a food lover, I often go to top rated restaurants and food tastings, so I admit I have high standards. Here is my opinion:

Positives:
Overall, a gorgeous setting and top top service.
A nice selection of various dishes characteristic of Oaxaca, including worm sauce and black mole... The crepes here are excellent, definitely recommend.
The ravioli with suckling pig also unique, through too salty.

Feels like an expensive 5 star restaurant, but actually is not that much more expensive than some of the other top rated restaurants in town, a good deal.

Negatives:
The food was excellent but not the best I've had in Oaxaca. I tried the black mole, it was complex but too sweet. Also some of the food had too much salt. I suggest ordering sauces (except for moles) without salt, and then add the salt yourself, to suit your tastes.

Overall Catedral is definitely worth a visit. If you are really really into purely food (over atmosphere), there are better places in Oaxaca. But if you want to experience a romantic beautiful setting, five star service and a classic restaurant experience, then this is the place to go.

Having read mostly glowing reviews, we chose Catredral to have our last night in this gastronomical centre, and it did not disappoint. Excellent service, delicious food and an attentive owner who has given up a career as a lawyer to return to Oaxaca to run the family business. Book in person to secure your table in the courtyard. The pork ribs were especially good: tender and flavourful.

We chose to go to the Catedral Restaurant on Sunday afternoon after church, based on trip advisor reviews. We were not disappointed! The price of 160 pesos per person, about $12.50, was incredible. The wide range of selections and all you could eat, fit the bill for our one meal out a day routine. Not only was the food delicious, but the service was superior. Oscar, our waiter was the best. I highly recommend the Catedral Restaurant, especially for Sunday brunch.

We were devastated that we only discovered Catedral on our last evening in Oaxaca -- otherwise we would have gone there every night. Having heard that Oaxaca had the best cuisine in Mexico, we'd been disappointed so far. But Catedral was a revelation.
It's in a beautifully restored old mansion, with a lovely indoor patio. Nothing folkloric here: the colours are deep and dramatic, and the ambience is stylish and sophisticated. As was the service. The food was outstanding; this is a long-established family-run restaurant which apparently bases its menu around dishes which the owner's mother refined from traditional Oaxacan recipes. It's very polished, and a different world from most of the "typical Mexican" tourist restaurants in town. A must if you're in Oaxaca...and don't leave it till your last day.