Mary's is simply just a good restaurant. Their pizza's are great and they have a large variety of toppings to choose from, you can even order stuff like eggplant, or baby clams & garlic on your pizza if you so choose.
The service is usually very good. Although if you come on a weekend around dinnertime, be prepared to wait awhile as it is popular.
They also offer takeout and delivery on most of their items. In my experience their delivery service is the most prompt in the early afternoon before the dinner rush hits.
The food is always top notch, and their other menu items (other than pizza) are just as good. Try their linguine with clam sauce, and their garlic bread. Mmmm.