It's hard to imagine a place on earth which more accurately embodies the idea of an untouched, unexplored, natural rainforest than the area of the Manu Biosphere. If you are looking for a new experience, a fresh perspective of reality, or just a chance to step back, this trip is the one for you. The program does a good job of giving volunteers a wide array of projects to work on, from animal research to building bio-gardens for local families. Days tend to be long but interesting, and the food and general facilities are amazing. There are many opportunities to see local flora and fauna (I saw wooly monkeys on my first day), and you really get a feel for what the area has to offer. Consider carefully if you are squeamish or easily grossed out, there are a good deal of bugs (I stepped on my fair share of cockroaches on my way to the bathroom at night), although this could be just the thing you need to get over your fear of ants. However, I did feel like it was more of a vacation and less of a service project. Additionally, the program is fairly pricy for such a short period of time.
Overall I was pleased with the program because it gave me a chance to see an amazing part of South America, however if you're looking for a hardcore service project or don't have a lot of cash to throw away you may want to reconsider.