This is one of the best attractions in Toronto. It's appropriate for all ages. All of the exhibits have easy to read kid friendly language. There's a ton of interactive displays as well and some crawl places that also make perfect photo ops. They even have some interactive tanks where you can get hands on (if the inhabitants are willing). On my most recent visit, I was able to get a manicure from from a cleaner shrimp!
The aquarium is one of the attractions that is open the latest (11pm on most days). This makes it a great location for a fun date after dinner. My favourite time to go is around 8pm+ as it avoids most of the family crowd.
The lighting and the music make the whole walk through the aquarium entirely magical. The Dangerous Lagoon and the moving carpet are a really cool feature of the aquarium. You get to be completely immersed in the moment without worrying about tripping over a small child.