I stay at the Buffalo Marriott at least 7 times a year and find it a really great place to stay. Everything is clean and fresh, the staff are attentive and usually pretty helpful. They offer free parking and shuttle service to the airport, so it is very convenient.
The restaurant is predictably expensive and only has a limited selection, but its ok, the water in the pool is way too cold and the hotel gift shop/store is pretty poor. But other than these very minor issues the hotel has a lot going for it.
If you are thinking of using this hotel as a base for your visit to Niagara Falls when the closer ones are too expensive or not available. Go for it, it is only a short 15 min drive to the falls (not sure if the shuttle bus goes that far), so as long as you have a car, you will be fine.