A great, big (and I mean spread out geographically), really fun place to take a family. After being begged for years, my husband and I finally gave in and agreed to a first time trip to the dells with the kids (6 and 10). I chose this place as a major attraction to bring them, owing in large part to the megabucks they must have spent on advertising. They were in every brochure or guide I researched, showing pictures of people having lots of fun, rain or shine, because of their unique status as an indoor/outdoor waterpark with an indoor/outdoor theme park. This is what sold me, as I wasn't sure what the weather would be like in early June, and I didn't know if I wanted to be stuck just shooting down waterslides endlessly at a waterpark-only venue.
That being said, the experience matched the hype. I think the day we spent there was by far the best single day of the whole trip. Being a family of two forty-something couch potatoes and 2 kids, we weren't necessarily looking for ridiculously high, heart attack causing, little kid vomiting slides or rides. The outside waterslides were slightly intimidating, but not so much that it stopped me (couch-potato woman), and I hauled my self up the hills and broke world speed records coming down (clinging to my ten year old daughter of course- I wasn't brave enough to go by myself- she's still blackmailing me over that one...)
The bigger tube slides were a total blast, and my whole family was able to enjoy the lazy rivers, both inside and out. The inside waterpark was a lot more fun than I thought it would be, with a nice lazy river (slightly tricky to get in and out of for us dumpy folk though), and kiddie water park that we had to drag our kids from. The wave pool outside was really cold and really powerful. You HAVE to keep a hand on the little ones, as my 6 year old kept getting sucked out to the deep end. This is probably a good attraction for the older kids and teens.
The outdoor theme park consisted of a lot of fun go cart tracks, some moderate sized roller coasters, and a small, 4 or 5 ride kiddie section. Combined with the water fun, it rounds a day out nicely to ride around on the tracks, then go get wet, then come back. I'm not sure the theme park could stand on its own without the waterparks.
The indoor amusement park is a little like a carnival in a building (shades of Old Chicago?) with moderate non-terrifying, but fun rides.
WARNING! Be prepared to walk.. and I mean WALK! This park is really a combination of several older mom-and-pop go cart and waterslide attractions from past decades, all with parking lots and empty space in between, resulting in large distances between some of the attractions.
Overall, a fun place worth the price.