For years, culture-savvy theater- and concertgoers have made Southpark their lobby before and after shows. Its location is so good, however, this Northwestern seafood grill can slip on its on high standards. Still, the special-occasion ambience of the restaurant's high-ceilinged dining room and cozy wine bar can overcome even the most uninspired salad course. Spicy gazpacho with bay shrimp, warm, juicy dates stuffed with cured ham and, of course, the requisite mussels, oysters, crab cakes and calamari round out the solid pre-dinner fare. As for entrees, stick to the specials: Southpark is famous for its fresh seafood. (JAD)