We visited here mainly just to go to the aquarium, however I was surprised at how much more there was, and how much fun the Ocean Expo Park was. Entrance to the park is also free, which was nice, and it has a great view of the ocean.
Besides the aquarium there were manatees, turtles, playgrounds, a beach, and dolphins. However the dolphin show was closed because it was November (we still had 80 degree weather and sun). Also, since it was November I have a feeling the park was much less crowded than usual, which was nice.
The only downside is that, if you're staying in Naha City, it takes about 3 hours by bus to get to the Ocean Park (we couldn't rent a car). However, we took the #120, instead of the #111. So the bus traveled along the coast, and we stopped for awhile in a small town to visit the beach and play in the water.
If you do plan to got to the aquarium, the Nago Bus Terminal, where you need to change buses for the aquarium, sells discounted tickets.
Also, be careful not to leave too late, as the bus stops running at a certain time. We ended up taking a taxi back to our hotel. Though we did work out a deal with the cab, so it ended up being the same price as if we had taken the bus.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.