As noted in an earlier post, the Monterrey Aquarium should be avoided when a lot of people are there unless one loves being pushed and shoved, having a splitting headache, and watching kids run all over the place and parents yelling at them, while rarely getting a good view of anything. But, when it is not crowded, it is said to be an absolute delight. Here's what to do: Arrive at the Aquarium no earlier than 1.5 hours before closing time; look in to see if it looks relatively empty; if not, head for the hills; if so, go in. Under this scenario, you often can get in without paying the $50/person admission charge.
The Aquarium is in Cannery Row. Whatever charm or interest Cannery Row had, it's long gone. And if you're there at meal time, get out. There are plenty of good restaurants in the Monterrey area, but the Cannery Row restaurants seem to cater to the same people who love being in a crowd of crying and yelling kids, and who don't mind waiting forever to get mediocre but not necessarily inexpensive food. And parking is expensive.