I agree with the other post, the view at the Fallsview Marriott is spectacular, the room was really beautiful, and the staff seemed to be friendly. The breakfast was a nightmare though, long lines, no tables, and the food line was right beside the kitchen entrance. The food was good, but it was total chaos! This must happen often. You should try the Courtyard Marriott, it does not have a fallsview, but is still close (right beside the Skylon Tower) and the breakfast is FANTASTIC! We go there often, and it is always consistent without the chaos, and we have been upgraded free of charge to a 2 room family suite at times. Nice pool, lobby, etc. Have fun and good luck!
Update: July 17, 2009- just came back from a quick 2 day trip to Niagara Falls- the Courtyard Marriott on the Canadian side was again very nice!
I took my family to the Marriott Niagara Fallsview in August 2001 and again in August 2006. We had a blast. Both times the highlights of the trip were the breathtaking views from our junior suite, the Maid of the Mist boat trip and sightseeing at nearby Niagara-on-the-Lake.
While I do remember long lines, the wait time was short. Considering the number of tourists wanting to dine with a view overlooking the falls, the Marriott staff did a fantastic job of making sure everyone was on-schedule. Don't take my word as final, checkout, Tripadvisor.com and have a blast!