I had a choice of going on Royal Caribbean's Radiance or NCL's Norwegian Sun. We have cruised on a spectrum of lines, from Carnival to Windstar, Princess and Crystal. I had the impression that NCL had a somewhat spotty reputation, but the itinerary going around the Horn was so much better than going down to Ushuaia and making a U turn up to Brazil that I chose NCL. And was delighted by the choice. The Sun overall provided an excellent voyage, and the variety of ports and Chilean fjords was even better than expected. The previous review gave a lot of good details about the ship and ports, so I'll limit myself to areas not covered.
First of all, if at all possible, get to Buenos Aires early. Very early. Tango is the national pastime, and we went to the obligatory tourist tango show at Esquina Homero - just so so. But we went to a milonga at Salon Canning. That was great. Lessons until 11 pm, then people start filtering in. At midnight the band arrives, and the party goes on until the wee hours. All LOCALS dance...some extremely well, some like me. There was a wonderful couple in their eighties that looked gorgeous dancing together. And a little old guy who happily buried his face in the bosoms of his much taller and younger partners. In BA, we took a cab and covered all the key sights in two hours - for $19 BUT while the taxi driver was a licensed tour guide, he only spoke Spanish. My Spanish was good enough to understand most of what he said, but would limit this recommendation. MOST importantly, we spent two nights at Iguazu Falls. This is a two hour plane flight from BA, and I had serious doubts about the wisdom of leaving BA to go there. But if you can possibly go, GO. Stupendous.
We stayed at the Sheraton - expensive, but a fabulous view of the Falls from the room. The best single highlight of our three weeks in South America. The food in BA is very reasonable and simply delicious. I don't often eat steak at home, but steak and a salad in BA was our evening meal every night,and never disappointed. Don Julio in Soho is a great example, but there are a ton of good restaurants in the city. Definitely not a place to be a vegetarian. And don't miss MALBA, the art museum. I'm not a major museum aficionado, but it's small enough to be enjoyable with enough good art for the art lover. Shopping in Soho made my wife very happy.