The Fallsview Sheraton was a great hotel/resort. You can't beat the location, the view of the falls from the room was exquisite, there are many food and entertainment options in the resort, 2 pools and direct access to the Fallsview Indoor Waterpark. I traveled with my family (5 people in all) and stayed in a standard double queen - the room was a little small, but we weren't in there except to sleep. The beds were very comfortable, but the pillows were flat. The room was clean, well maintained and had a coffee maker (not the best coffee or fixings) and decent mini-fridge. The staff was great - everyone we encountered was very nice and engaging, and also accommodating and knowledgeable.
The resort is BIG - expect a lot of walking, especially if you park in the garage. This was perhaps the biggest negative. It took 10-15 mins to walk to and from our car (and in high traffic times even more) with most of the delay waiting for elevators, but there was also a ton of walking. However, if you're in Niagara Falls, you expect the walking.
We will definitely consider staying here again.