I've been twice-----my wife is from the south of Chile (Valdivia).
I've been to 38 countries and Argentina is one of my favorites. Great people, best steaks in the world, great wine, spectacular scenery and its still pretty cheap.
Buenos Aires is a great and interesting city. Mendoza is great for 2-3 days. The south is awesome and has lots to see and do..
PM for more specifics.