U.S. side or Canadian? I have only been to the U.S. side 1 or 2 times. There is a viewing area and casinos.
Even though I am from the U.S., I find the Canadian side and Horseshoe Falls much more enjoyable.
Crossing the Peace Bridge at Buffalo, you can take the Q.E.W. to the falls passing by Fort Erie horse race track and an amusement park. A better option is to take the scenic Niagara Parkway.
At the visitors center you can take the Journey Behind the Falls, walk along the falls and gorge, or take the Maid of the Mist. There is an incline that runs from the Visitors Center to the hotels, restaurants, and the great views of the falls on Fallsview Blvd. Clifton Hill has plenty of restaurants (my wife's family used to go to Mama Mia's in the 70's) and tourist attractions like Ripley's and wax museums (and casinos). Lundy's Lane is home to miniature golf, water parks and other typical tourist activities.
If you have any extra time you can head out to the wineries near Niagara on the Lake. If you have a lot of time, head to Toronto. What trip to Canada is complete without a stop at the Hockey Hall of Fame?