This is a beautiful area, and a place to visit for many. But note that it is pretty steep to walk up there, so make sure you are in shape to do it ;-)
Coming up to the waterfall, we just sat there for an hour enjoying the view. Superb!
After that we walked up to the old farm ("støl" in Norwegian), which is also a very nice place next to the river leading to the waterfall.
Absolutely I recommend you to visit this place.
But, if you are taking with you young (and enthusiastic) kids, make sure to keep an eye on them and let them understand the dangers. There are no fences, and it would be a long fall...

Traveled from Stavanger to Maanafossen. The drive up is nice. Lots of nice scenery to see along the way. You need to be there early, because there's a limited parking space. And they will be taken quickly. The hike up was a bit hard, but I managed it. When I arrived at the destination, the view was fantastic. We had a nice view over the falls and surroundings. I was a little tired when i finally got back to the parking.. Only thing to complain about was the toilets. This was the open type, so it smelled bad. This was the general opinion of the tourists. Don't forget the camera and video for this trip. And also have a pair of good shoes. It can be a bit slippery if the ground is wet.