I chose the cruise based on itinerary as I do all my travel. The trip down the Amazon was great but not as good as I hoped. I have been on the Amazon in Peru and perhaps because I stayed in a lodge on the river it seemed to capture more of the "spirit" of the place better than the shore excursions I had.
I liked most aspects of the cruise and would recommend Oceania to friends. The one area where it was deficient, in my opinion, was shore excursions. I had 4 for free and I bought one to use up on board credit but they were not great in general and not worth the price (if I had been paying for them). I was on three of private tours that I found out about on Cruise Critic and they were better tours and better value. I prefer to be active on tour (e.g. biking or walking instead of sitting in a bus and only getting off for photo stops (or even worse, shopping)) but there were few opportunities for that.