This is real Mexican food. If you're a first timer, you're going to want to try some of what you think will be good. Lemme save you the trouble--don't. Just get the al pastor tacos. It's a marinated pork combined in spices and chiles, and Tacos El Gordo does it fantastically! It's cooked to perfection. You see them cut up the meat in front of you similar to how you'd see shawarmas prepared. Meat is full of flavor and moist.
I've also had the lengua and the carne asada. Carne asada is fine, it was slightly on the burnt side for me and the lengua was meh. I'd recommend getting the al pastor over anything else.
Next time I have got to try the mulas, which are like mini quesadillas sandwiching your taco of choice. I heard great things about it after I ordered.
TIP: Look at the signs and line up in the line with the al pastor tacos! That is where you order your al pastor. The signs tell you which line have which items. Follow that.