While the food at La Mestiza is decent, the prices are not. If you're looking for cheap, delicious tacos, I'd recommend Taqueria Guadalajara instead.
The atmosphere of La Mestiza is rather pleasant. They have low lighting in the evenings which makes the warm colors of the walls and decorations glow. The entrance way is blocked off by hanging tapestries so the cold doesn't blow directly into the restaurant which is nice as well.
My friend and I ordered relatively soon after sitting and our food came out in a timely manner (right as we finished our chips and salsa). I got the Trio de Taco (I ordered all steak tacos which is a dollar extra) and horchata on the side. The tacos were decent; nothing to brag about, but not bad either. However, I did not think they were worth $9. The horchata seemed to have more cinnamon than I'm used to, but that was fine with me because I love cinnamon. I was surprised that the glass my friend's margarita came in was the same type of glass that my horchata came in, not a true margarita glass.
Overall, this restaurant was just so-so. It was a nice atmosphere to eat my food in, but I would prefer the cheaper and more flavorful food at Taqueria Guadalajara.