I really enjoyed the hike in this park.
It is true that the entrance fee is little pricey. I think you even pay by person and not by car but I am not 100% sure because I got there early in the morning and there was no one at the entrance.
I started at the nature center (trail 1), hiked through trail 2 to the cliffty falls. Trail 2 was fun 'cuz I hiked through semi dried creek bed. I didn't mind uneven surface, stones and wet rocks and some water but it could be a potential minus for some.
I returned to the nature center via loop and it took about 4.5 hours of semi- fast walk.
It was a very hot day but since it is mostly shaded by trees, it turned out to be a great hike.
Don't expect to see any great falls, maybe after a rain but what I saw was only tiny falls but still it was really pretty.
There is a tunnel / cave like area you can go through an explore during certain parts of the year. Check the below map for details.
Afterwards I went to downtown Madison to check out the place and had a bite to eat. It was a nice trip.
Below is a map for your convenience if interested:
http://www.in.gov/dnr/parklake/files/clifty_falls_trail.pdf