If you like losing money, you'll lose more of it at Casino Niagara than you would betting on the Giants.
The restaurant with the best view of the falls is the surprisingly named Fallsview in the Sheraton Hotel. A little expensive but the food is ok and they do a decent lunch buffet. There's a bunch of decent restaurants in town:
http://www.urbanspoon.com/n/242/46294/Ontario/Niagara-Falls-restaurants. The pho is so nummy at Pho Xyclo. Savoury and Sweet does a mean schnitzel, and their french onion soup rocks.
Try the Niagara Skywheel - you get really great views of the Falls on a Ferris wheel-type dealie. Of course if you want to get up close and personal with the falls, sign up for the Maid of the Mist boat thing which'll take you right up to them.
If you have kids, take them to the Nightmares Fear Factory. It's scary cheesy fun, and for more creepiness check out the wax museum. Lots of other things to do like the Bird Kingdom and Whitewater Walk etc. I'd recommend going on Street View and "driving" around the city getting to know the layout and where all the good stuff is so you can prep an itinerary before you get there.