Tom Sietsema beat me to the punch; I've been meaning to post a mini-review of MXDC since we tried it last week. In a word: bah.
The food was very, very hit or miss. I really liked the cochinita pibil, the chips and salsas, and the fresh homemade tortillas. However, the "arepas" were inexplicable and awful: like hollowed-out, toasted hamburger buns (??). We left them on the plate. And the gazpacho was simply inedible: grossly acidic and oddly flavorless. We also left it mostly uneaten. The mushroom/huitlacoche tacos were fine: not amazing, but not bad.
We found the space somewhere between uninspiring and downright hostile (noise volume is off the charts, and we are not particularly noise-sensitive).
The prices are very high - likely due to the prime real estate, but certainly not the ingredients. The staff was uniformly very nice and competent.
The next time I want Mexican food in a slick downtown setting, I'll stick with Oyamel or Rosa Mexicano.
Anybody else have MXDC experiences?