I've been to the aquarium numerous times and am very impressed with it. I went recently at 10.15am and there were a number of school excursions there. I think it is wonderful for the children to be exposed to the animals but if you are a full-paying guest it is very noisy and often difficult to see the exhibits. I would try to avoid between 10am and 2pm on school days as it is very pleasant out of these hours. It is well worth visiting the aquarium to see the aquatic animals around Australia. The combined pass is better value, if you buy on the internet before arriving there is a discount worth considering and often in some of the tourist magazines there are discount coupons.
if you are going to have a meal you may like to consider the Helm Bar which is nearby where the meals are reasonably priced and delicious with a beautiful view over the water.
If you own or manage Sea Life Sydney Aquarium, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.