The Bottom Line: Authentic, flavorful tacos in a "hole in the wall" style restaurant. Just be willing to put up with a line.
Try:
Asada
Sudadero
Pro:
There's little else to be said except they make excellent tacos, fast. Definitely a great place to pop by for a quick snack, and they have a good variety of meat. (Not good for vegetarians)
Con:
The lines are long, especially for their more popular meets due to their unique ordering system (lines by meat type). The place is very dingy, but depending on your point of view, can add to the authentic experience. It's a little pricy for what it is, but decent for Vegas.