DR Cillaliz - Richard and I were taking the 3-hour cruise all the way around Manhattan last October when you and DR jhvw were traveling to NYC. We thoroughly enjoyed it, but for a first-timer, the 2-hour might suffice.
And I agree that seeing the Statue of Liberty from the Staten Island Ferry is adequate. Back in 1999, we told DS Rob that we had time to do one major sight before meeting DR Elmore at the much-missed Barrymore's and he chose going to the S of L. Having previously seen it from the S I Ferry a couple of times (which is breathtaking), I concluded that I could have gone my whole life without ever actually going there. And, we almost got marooned on the island by a thunderstorm, which made us late for dinner with DR Elmore.
If you do ride the Staten Island Ferry, I recommend taking along a snack of Hershey's dark chocolate and bing cherries. That's how my mother and I did it on my first trip to NYC - 40 years ago. She and I repeated that culinary tradition in 1987 when we took a San Francisco Bay cruise that took us out under the Golden Gate Bridge.