We spent a full day at the Ocean park and I'm pretty sure I could have spend a couple of days exploring the place - I LOVE aquariums and lucky for us the weather was brilliant. In fact I intentionally chose Okinawa for some fun sun times, even though November is one of the cooler months, the temperature was still pushing 30 degrees which is heat wave temperature in my books!
In order to get to the Ocean Expo Park from Naha, you either need to take the bus or hire a car. We took the bus route as to avoid driving with some severe jet-lag, otherwise from what I saw, driving around Okinawa should be fairly simple, highways don't get too fast and they drive on the same side of the road us so definitely a good option for next time when I decide to take a longer relaxing holiday there! :D
The quickest bus is the Yanbaru Express Bus - there is no English on the website but I used google translate to find times and prices, it took us roughly 2 hours to get there and it cost us 1900 JPY per bus ticket (about £14).