We rode the sea rocket during our vacation in July 2012. The ride is $18 per adult but kids (under 12) are free with a paying adult, so the price for the family was reasonable.
The boat ride is approximately 50 minutes long and goes from the inlet (end of boardwalk) up to around 130th street. We got to see a school of dolphins and the captain did his best to make sure everyone on each side of the boat got a view of them. The ride was entertaining but expect to get wet, especially in the back of the boat. I will definitely do this again when I'm in Ocean City.
I would recommend arriving early if you are driving because the lot is very small and fills up and closes. There are other lots in the area but down at that end parking can be a challenge.