Just got back from visiting the Canadian side, spending 3 nights in NF itself and 3 nights in Niagara-on-the-Lake, with a car.
1. The falls are spectacular, and everyone should see them at least once.  

2. Pre-purchase the Admission Adventure pack from AAA before you go: Maid of the Mist is a must-do, White Water walk is fine, as is walk behind the falls.  The transportation pass for (any) 2 days is VERY useful.  Whirlpool cable car and Power Station visit (discounted with the pack) are worth doing.

3.  The town of Niagara Falls has been very commercialized and built up - but at least it is clean and modern (not like Atlantic City, for example).

4. We stayed at Sheraton Fallsview, paid a little extra for rooms with a view, which were SPECTACULAR - even our cynical teenage kids were wowed.

5.  Eating and drinking in NF is a complete rip-off: expensive, mediocre (at best) food.

6.  We really liked Niagara-on-the-Lake: pretty town, some very good restaurants - same sort of pricing as NF, but completely different league in terms of quality.  Shaw theatre festival was great - 6 different shows a day, quite pricey to pre-book but there are often same-day tickets available from the box office for $25.  Loads - no, really, LOADS - of interesting wineries all around the area.  Local wine is fine, perfectly drinkable, but nothing really world-class (that we found).  We stayed at Best Western Colonel Butler Inn, which was fine.

7. So, next time: I would spend the whole week at Niagara-on-the-lake, and pick 2 days with great weather to do the falls, if possible one of those days being a fireworks day.  I would drive the 5 minutes or so up to Queenston Heights, park there, and use the free travel pass to get on the bus and do the Falls sights.  For the fireworks night, I would go and park in one of the Casinos.  Doing it like this would enable weather optimization (you can visit wineries or go to the theatre easily in the pouring rain) and minimize the sensation of feeling ripped off in commercial NF.

Enjoy! 

Recommended: Yes

Best Suited For: Families
Best Time to Travel Here: Anytime