I'll be honest, I really don't how to authenticate Mexican food. I can only tell the difference between Taco Bell (which I always refer to as "Toxic Hell") and localized Mexican restaurants in my area. One of which I visited last Sunday, (which is before I joined this forum; kudos to sailordragonball for wanting me to join), called El Niagara in Woodstock, IL.
No need to order an appettizer, just showing up gets you home-made (if not, pretty close to homemade) chips and fresh, slightly tobassco-hot salsa. To drink, a coke which was served in a cold can, but a glass of ice was brought with it.
Normally I'm adventuresome with selections, but I decided to get a beef-stuffed burrito. It came with Spanish rice, and refried beans with lettice and sour cream on the side. The burrito itself had a very, very thin layer of cheese on the tortilla, (I'm guessing motzerella).
The place was not crowded, nor was the music loud. Just a nice little restaurant. Not a bad place to go for good Mexican food.
J.T. Schrader