I've been to Worlds of Fun about once a year for the last 10-15 years, and I still enjoy it. The important thing to understand is WOF is not in the same league as Cedar Point or some of the Six Flags parks in terms of number of coasters. They have added two top-notch coasters in the last 5 years (Mamba and Patriot) which are pretty much worth my three hour drive.
The smartest way to experience the park is go after 4 pm. Not only will you pay a discounted fee to get in, but most of the people who arrived when the park opened will be leaving. In the summer months, you'll also get the added bonus of missing brunt of the heat & humidity. If the park is open until 9, five hours is plenty to ride most everything at least once.
Now for the complaints: the park is owned by Cedar Point, but the WOF ride operators are not nearly as efficient as they are at Cedar Point. It's common to see open seats on rides and to wait while they get load and unload the rides.
Also, the last time we visited (June 2007), all of the restrooms I entered reeked of a mold/urine/body odor combo that was quite overpowering. The KC area had a pretty good downpour the night before our visit, so I'll give the benefit of the doubt, but it was not pleasant.



