Rosa's is my new go-to Mexican spot in town. Service was slow (seemingly for all tables) or else I would give it 5 stars. Don't judge a book by its cover (or in this case, it's semi-seedy strip mall location).
Definitely ask for the hot salsa as the other two are sweet as other reviewers have mentioned (we mixed the sweet ones with the hot and enjoyed them all). The horchata was really good (and includes unlimited refills, which I found odd for a horchata... note - more than one will really fill you up).
Portions were large and tasty and great as leftovers the next day.
If you have enough room left over (or a lot of friends to share with), give the fried ice cream a try (I have been trying to find fried ice cream like this since moving to Phoenix from Denver in 2001!).