From the couple I've seen:
1. Monterrey Bay Aquarium-it has a little bit of everything, takes most of
the day to see it all.
2. The Shedd Aquarium in Chicago-lot's of fun, can easily see everything
in an afternoon. They have divided all the waterways in different
sections. The newest section is the Amazon basin which has fish as
well as birds in some of the same displays. As you travel around you
are supposed to see a whole year in the life of the Amazon as the
water floods the surrounding flood plain & then recedes back into
it's banks.
3. The Steinhart Aquarium in Golden Gate Park-I agree some of the
displays are a little dated, but the Penguin display was fun, the
penguins would come right up to the glass & interact with you. Can
easily see it all in an afternoon plus do some other things in Golden
Gate Park.
4. The Texas State Aquarium in Corpus Christi-it's OK, especially if you
happen to be in Corpus Christi & have an afternoon to kill plus there
is an old Navy ship next door that you can walk on, that's lots of fun
for the kids.
Now granted, some of these aquariums I saw 2-10 years ago & they have
probably changed & updated things. All in all I thought it was time well spent going to any of the aquariums.