Villa del Sol offers up passable Mexican food in their brightly colored dining room, or out on their veranda. Their College Street location is very convenient to my hotel, so I have been there several times.
I could describe Villa del Sol in a single word - "variable." One day, the service is constant and attentive. The next day, it's difficult to flag down a waitress. Some days, their food is creative and tasty, and other days it is one step down from Taco Bell.
They do have a great menu for a Mexican restaurant in New England. There are plenty of choices for the low-carb dieter, because it isn't all tortillas and rice. They do have a few interesting shrimp dishes. They also have all the Tex-Mex schlock that Americans have become accustomed to. Their specials are far better than the rest of the menu, which is, I suppose, what makes them specials.
Villa del Sol also makes a good and inexpensive margarita. You can definitely eat here, have a drink, and stay within your per-diem. Diners often get a free dessert on top of their meal.