DD is fairly large. You have the Marketplace with many of what I would call traditional Disney shops - toys, clothing and other items with Disney characters plus several restaurants - and then there is DD West Side with other stores (Virgin Records, magic shop, AMC movie theater), restaurants (House of Blues, Planet Hollywood, Bongos) plus DisneyQuest and Cirque du Soleil. Pleasure Island is also right there as well.
If you have never been there before, I'd plan on a couple of hours to check out everything. If you have time, I'd also recommend taking the boat ride from DD to the Port Orleans resorts (Riverside and French Quarter).