Because NYC is a homeport for me, I've never had to deal with excursions there. But I do look to see what they offer, and nothing looks that good to me. I don't recall seeing an Ellis Island trip. OP, I'm sorry that was cancelled. it would have been worth your time. Cunard should offer more trips wtih a single focus, considering the time constraints.
For anyone who is considering one of Cunard's NYC excursions, I suggest you avoid the bus and "three stops" tour. I was just on the 14 day Canada cruise, and my table companions all had been on since Southampton. One woman said she did this tour, and there was no guidance other than when to get back to the bus. The stops were:
1. "Central Park and an art museum" (her description). This was the Metropolitan Museum of Art, a terrible choice for an hour or so--it's huge! I don't know what I would choose to see in only one hour. I spend much longer than that when I go. She said the queue to get in was so long, she just went for a walk in the area.
2. Rockefeller Center. It's a chance to see an iconic part of Manhattan, but not a lot to do other than look around.
3. "Somewhere to see a church." Again, her description. From what she said, I guess it was near Trinity Church in Lower Manhattan.
To be fair to the tour, she got on the bus with no idea where she was going, but even if she had done some research/planning, it didn't sound like a good use of a day in NYC.
