My wife and myself start our Indonesia trip in Kalimantan's Tanjung Putting National Park by the end of past June; although the rest of the journey in the other islands was great, both agree the days we spend in the National Park were the most extraordinary experience.
Orangutans, proboscis "long nose" monkeys, macaques, water snakes, crocodiles, kingfishers, nice sunsets, nights with trees plenty of fireflies, sunrise hearing thousands of jungle sounds, etc...
Everything in a small "klotok" boat, detailed explanations of the native guide, which love their Island, the park biodiversity, and specially these "almost human" orangutans.
Most important; they have a mission to work for in Kumai, protect the orangutans environment in Borneo, thank you very much for let us feel as part of it.
As conclusion, we highly recommend everyone visiting this paradise, be sure your trip will be memorable.