If you are able to be there on time (by 4.30 pm) you can enjoy the sunset cruise of Brahmaputra river. Make sure you stand in the queue in advance and get the front deck seating to soak in the vibes!
This is anything but a zoo, a super open space where you can take a cycle on rent and explore..make sure to reach early morning by 9 am so you can enjoy it without too much crowd.
You can easily spend 3-4 hours exploring the various cultures and tribes not only for Assam but entire North East! Keep a day aside for this amazing place. It won't disappoint, I promise!