My family did the sunset dinner cruise lead by Captain Kauai and his crew. The whole crew was great. Extremely helpful and courteous. Capt. Kauai, being part native Hawaiian, is knowledgeable about the islands and traditions.
The views are definitely something.
However, the waters along the coasts are quite rough. If you have any tendency to get seasick, you should prepare ahead with prescription strength medications. On our catamaran, there were at least five passengers throwing up. My wife and kids took Dramamine beforehand and my wife still couldn’t handle the cruise. The kids were complaining of general discomfort, but were able to keep their food down.
Also, no shoes allowed on the catamaran. And bring towels even if you aren’t doing snorkeling because the ocean water will splash in. An umbrella might be helpful too, since you never know with the Kauai rain.