I have visited this place many times with tour groups.
The main reason most people come here is to easily see Orangutans in a relatively natural rainforest setting. Food is put out at a platform every day at the same time, and the animals are free to come and go as they please.
Because there is very well developed and undisturbed rainforest around the orang-utan centre, there is also good bird and other mammal watching.
Recently, a new enclosure has been built to house sun bears, a small bear native to south-east Asia.