The basic point is, don't expect Mexican food in Mexico. That is, don't expect the Tex-Mex taco fare you're used to in the United States.
I loved trying the food in Guadalajara when I visited there a few years ago, particularly the discovery of chilequiles and cheese-stuffed tortillas for wrapping meat and vegetables.
Mexican food in the States is so predictable, isn't it? I know I'll always find pretty much the same style of fajitas, tacos, burritos, enchiladas and quesadillas, with sides of refried beans and rice, right?
But what about huevos divorciados for breakfast? (Yes, those are indeed divorced eggs.)
Half the fun I had during my most recent visit to Mexico was learning about all the variations in Mexican cooking and the foods at Mexican markets. My favorite find ended up being those chilaquiles, also the favorite of the writer of the BootsnAll post on Mexico.