I'm a member of Mystic Aquarium and am biased, but I think it is one of the best in the country and I have been to about 10, including Chicago and Monterey. It is especially good for kids: hands-on, up close. They have awesome contact programs with beluga whales and penguins which you have to pay for but are totally worth it. Also, deep sea explorer Bob Ballard is based there and has a whole exhibit of his Titantic discovery and much more. Why do you say it is small? Maybe it's because a lot of exhibits at Mystic are outdoors as well and indoors and most aquariums are all indoors. Anyhow, go there! It's about 25 minutes from Mohegan, and Mystic itself is really cool.