I give La Mestiza five stars because I've been there over a dozen times and still want to go back regularly. It's definitely one of the two best Mexican restaurants in Madison.
As other reviewers have already commented, their homemade chips are the best I've had anywhere in the country. If you go there for lunch, one of my favorite's is their Tre Tacos. The pastor (pork) is the best but all three are quite good. I usually get three pork tacos though since the swine is the king of all meats! Oh, and speaking of pork, on Friday nights, their weekly special is pork shank with cactus. It's one of the best meals in Madison for the price!
La Mestiza's flavor re-kindles memories of going to a Latino friend's home and being treated to the skill and knowlege of generations of mothers and grandmothers. If you like authentic Mexican cusine, check them out.