Thrillville has a massive variety of gameplay contained within it - you can be shooting robots one minute, then doing a dance game, then driving go-karts, and then doing a marketing campaign or taking out a loan for your park. One big design challenge was how to fit all that into a whole that didn't feel hopelessly forced or disjointed and pointless.
Above: The images used here are from the PS2 or Xbox versions of the game. Mileage may vary on PSP, though gameplay should be the same.
The setting for the game came to our aid here - if you think about it, a theme park is exactly a massive array of varied, fun experiences, so the whole setting for such variety in Thrillville is naturally "right" and not forced or contrived. The only thing left for us to do was to tie everything together so that there is a point to you doing all the different cool stuff. The reason you do things, apart from fun, is driven by the story, and when you've finished a game or mission, you get a reward that helps your overall objective of managing your park.