We did the overnight Doubtful Sound cruise with RealNZ. We were nervous due to some sketchy weather and were worried we spent a decent chunk of change for nothing. We couldn't have been more wrong!
First, huge hat-tip to the crew. The young ladies (Molly, Ashley, Hannah, and Grace) were attentive, super friendly, knowledgeable, and service oriented. It was fun to see how genuinely excited they were to experience the Sound's teeming waterfalls. The captain (Riordan, I believe) had an open bridge policy and we chatted with him for a while. Super nice guy and an incredibly experienced sailor. The cook (never caught his name) made delightful meals from scratch, as well as all kinds of snacks and other treats.
The sights are amazing. Do the overnight tour for more time in the Sound to ensure you see as much as you can. Jump in the kayaks even if it is raining. Eat as much as you can.
This tour was professional and worth every penny. NZ has a lot of highlights, and this is certainly one of the best.