Culture shock? - I don't think so.
I would have loved to have travelled around Argentina a bit more, but had no possibility of having enough time this trip (so a good excuse for another trip
). I liked Buenos Aires a lot, but like you say it doesn't feel like really is South America (not that I have anything much to compare with) much more European.
I can see myself going back to Isla de Pascua for a couple of days to refresh the batteries in the middle of future big trips, much like I try to fit in a visit or two to other south pacific islands each year.