If you're in San Marcos, it is easy to find a Mexican Restaurant. However, most of these are open 24 hours and places whose atmosphere is no better than a fast food joint. If you really want to go out on the town, Acapulco, in Restaurant Row, is much more appropriate. The atmosphere is festive and the food is so-so. The prices, however are pretty cheap. It has mariachi bands on the weekends and don't miss Margarita Monday for cheap drinks. At night the bar also turns into a club. You can sit inside and out, it has been a pretty regular restaurant for my family to visit. It caters to pretty much all ages, and is always a nice place to go if you don't want to be all fancy. It also is right next the movie theatre, so you can head over there after or before. RATING: average
if you want a more upscale mexican restaurant check out Mi Guadalajara in Escondido.
if you want a more downscale mexican restaurant check out Jibertos or Santanas or Oscars in San Marcos.