This is the best authentic Mexican restaurant in Madison. My wife and I have been to many other Mexican places in town a none compare to Tienda los Gemelos. The food is delicious and cheap, what more can you ask? The service is really friendly. The place might not be the nicest but it's decent. It's family friendly though.
I recommend coming on weekends as it's the only time they have carnitas and barbacoa available as a meat choice for any plate. On regular days they only have steak, chicken and chorizo. I ordered a gordita and sopes. Both were full of meat. My picture is a little deceiving as the gordita looks kinda empty but believe me it was full of delicious carnitas. They also offer chicharrón as an option for your food. For those who don't know chicharrón is pork crackling, it's oh so delicious! This is the only place I've found in town that makes chicharrón. The one thing that struck me as odd was that they don't have guacamole which brings me to my next point -- their great service. They offered to make guacamole for me even though they didn't have it on the menu. They also prepare your food really quick, I think we waited less than 10 minutes for our plates.
I've already been here twice and plan to keep coming back for their great food!