There are a few I would recommend. Primavista on the west side is a good choice. Great Italian food with a wonderful view of the city. Another romantic restaurant with a view is the Celestial Steakhouse in Mt. Adams on the east side of Downtown. Downtown Cincinnati diners can't go wrong with Orchids at Palm Court in the Hilton Cincinnati Netherland Plaza. Orchids and the Netherland are beautiful art deco gems; romance is in the air with the old school vibe of high class dining from the 1930s/1940s. Plus, Orchids is frequently rated among the top restaurants in Cincinnati. Another top-rated Cincinnati resturant is Nicola's in Over-the-Rhine; Nicola's is an excellent choice for a romantic dinner with fabulous Italian food.
