One word: Margaritas.
I love the margaritas at Los Olivos. I've only had a cheese crisp and a bean burrito here, so I can't speak volumes on the food (although both were good) but I can't say enough about the chips, salsa and of course, margaritas.
Happy hour is fun there- it's never so packed that it's annoying and the service is pretty good. If you like cheap drinks and good Mexican food, definitely give this place a whirl.