Never get the rita's at Zippy's or Moe's... they are BAD. They food is pretty good though. Far from authentic Mexican, but good.
Like anyplace, they have good menu items and average menu items. Tacos, Burritos, and Nachos are built the way you want them, so its hard to go wrong. It's a good place to have some happy hour beers with chips and salsa.
Unlike the other mexican short order places around here (izzos, moes), Zippy's actually puts spices in their food. So if you are a person who likes the bland food, don't go there. If you like good, spicy food, go to Zippy's. I for one can't stand izzos or moes because it tastes like I'm eating a big tortilla full of nothing.