The official wedding hotel is located at Rockwall Harbor, which provides many things to do just steps from the Hilton! There is a movie theater, boat rides, and many dining and shopping options all on the lakefront.
The historic downtown square is just a quick drive from the Hilton. There are many boutiques to browse as well as many great restaurants. Zanata and Bin 303 are both very good.
If you are coming to town early and have time for sightseeing, Downtown Dallas is worth a visit. There are great museums downtown. Some of our favorites are the Dallas Museum of Art, the Perot Museum, and the Sixth Floor Museum, but there are MANY more. Klyde Warren Park and the AT&T Discovery District are both pedestrian-friendly areas with food and drink options. The Arts District has several great breweries, a bowling alley, and a cidercade (cidery + old-style arcade). It's a great downtown neighborhood to visit solo or with a small group.
If you have extra time in Dallas, and you REALLY want a stereotypical "Texas" experience, a drive out to Fort Worth to see the stockyards is worth your time.