The scenery and adventure of being in this part of the world are unparalleled. Good destinations, although you'll want to go far inland from Puerto Montt to see the gorgeous lake district of Chile. We did not use any HAL excursions, instead booked through South Excursions in all areas but Brazil. Virtually the same excursions for a lot less money.
Ship sails leisurely thru fjords and "glacier alley", a welcome respite from the rough ocean waters. We spent hours on our deck, taking it all in. Our group loved Ushuaia and nearby Tierra del Fuego National Park. Punta Arenas has its charms but you'll have to look very carefully to see a fantastic exhibit: a replica of Magellan's ship. It's near the ship docks, but has poor signage; even our cab driver didn't know where it was until we showed him on a map.
All the cruise is weather-dependent, so don't be sure you'll be able to stop at the Southernmost ports or be able to cruise past Cape Horn. We did see the Cape on an unusually clear and peaceful day, but the weather is tricky even in summer. Bad weather in the Falklands meant 4 straight sea days and everyone was getting pretty restless by the time we reached Buenos Aires. We had some very rough seas to deal with. Not counting the unscheduled sea day, we thought there was a good combination of lazy days and port days.