My mom just got back from there 3 days ago. My son started his summer break and I had no daycare, so my parents took him there for a short trip. He is 11.
They stayed at the Embassy Suites Fallsview and really enjoyed it. They were right next door to the Marriott and said it was equally as nice. Be warned though, some of the rooms in the Marriott can be *viewed* by some of the rooms at the Embassy Suites. My son got an eyeful one evening of some apparent "honeymooners." Fortunately, it was only a PG-13 rating, but he hasn't stopped telling everyone about it yet.

Keep your curtains closed!!!!
Anyway, my son LOVED Maid of the Mist. They had to do it twice. The did the Behind the Falls tour which he liked okay. He was against going to the Butterfly Conservatory, but my parents made him and he liked it a lot.
They also did Niagara on the Lake. My parents liked it, my son was totally bored.
Then they did the IMAX show about Niagara Falls and that was very good.
My son wanted to do the Whirlpool Jets and the thing (gondola??) that goes between the falls, but my mom was having no part of that!
Food was VERY disappointing. I had read this on
www.tripadvisor.com and warned her. That a tough time finding places to eat. If you do some reading you will see that all the typical chains are there (TGI Fridays, Outback, Rainforest, etc) but the food is apparently horrendous and very expensive. Doesn't make sense but I got consistent feedback on this. Apparently the pizza is good. My family ended up going to Boston Pizza. My mom agreed that the pizza was very good but the service was VERY poor. They did try to go to Wolfgang Puck's one evening--that looked promising. But my son has a peanut allergy and there were cross-contamination warnings there so they felt it probably wasn't safe for him.
They ended up staying 3 nights there. On the last day, they checked out and went over to the Great Wolf Lodge (which is closer to Niagara on the Lake). It was actually a bit cheaper than the Embassy Suites but did not include breakfast. They all LOVED this place and it is right up there with Disney quality. My parents were very impressed with this indoor water park and my son loved it. They also said that they FINALLY got some good food there. The restaurant has a very nice buffet. They also have a table service restaurant but my son was getting pretty fed up with that at that point. The hotel just opened in April so the rooms are very nice and beds are still comfy.
If you have kids you might REALLY want to think about doing one night here!