I went to Casa Merlos after reading a glowing review of this place in this Message Board. Do a search on "Great find in Mexico City - long".
Whoever posted that review was right on the mark. I had my best meal in Mexico City - by far. I can't even find the words to describe the experience. Possibly one of the best meals I have ever had - and for a fraction of the money I have paid elsewhere.
I sampled most of the dishes recommended in the long review I noted above (which has the address for this place). They were unbelievable.