We did this trip in reverse on a Celebrity ship last winter and LOVED every one of the 14 days and even enjoyed the excitement of 45 foot seas as we neared the Straits of Magellan. Each port of call was interesting -- penguin lovers were really excited by all the options to see these creatures. We sailed in early Feb and absolutely FROZE on the Falklands. We needed our Canadian gloves but our gortex jackets left us shivering.
We considered it a great cruise as it was enough to simply dabble in a ship excursion at each port of call.
On our own we had 2 precruise weeks in Peru and Chile and another 2 weeks in Argentina and Brazil where we really enjoyed touring.
I'm sure you'll really enjoy your South American adventure.