I've been to Santa Claus land (the original name of Holiday World) quite a few times over the years, beginning when I was 3. I still have that first picture with Santa Claus! Holiday World may not be the biggest amusement park, but I think it's one of the best. They've got top-notch roller coasters, and other rides, with a variety for different ages. The water park is a lot of fun, with different rides and the wave pool and lazy river are great places to spend a hot summer day. The park is the cleanest amusement park I've ever been in, and we've visited parks from coast to coast.
The price of tickets at Holiday World is a lot less than at other parks, plus they have all sorts of opportunities for discount tickets. Check their website for discounts!
They offer free sunscreen in the water park, and free soft drinks throughout the park, which is big money saver. Parking is also free, which isn't always the case at amusement parks.
The owners seem to really care about the visitors to the park. On a trip there 6 years ago with my kids, we were rear-ended by another driver. We decided to continue on to the park, and I just happened to mention the wreck to the person at the ticket booth. The Kochs (the owners) came out to check on us, had us looked at by the first aid people, and gave us vouchers for free meals that day. They said that they wanted to make sure that the rest of our day was better than the drive to the park.
When you leave the park at the end of the day, you will most likely be told "Bye" by one of the Koch family.
Have fun!