A tad overrated.
Is it delicious? Yes. Is it muy autentico? Good question. I've been to Mexico a few times and the food that the locals eat away from touristy areas seemed more gringo-ish than this.
I will say that once you wait in line for 15 minutes and then pay way too much for street tacos, you are treated to spicy pork deliciousness. However, I think $2 each for small tacos and long lines with little seating is too much for me to give Tacos El Gordo 5 stars.
I took a buddy who I thought would like it and he wasn't impressed at all. Same complaints as me. Too long of a line, fighting for a seat, too expensive for what it is. But damn, those spicy pork tacos are good.
Tip-if you are really hungry, order the fries and two tacos=tons of food for $14.