The minigames give Thrillville rich variety. We had to be careful with these, though - without special care, it would have been easy to make them very shallow and not very fun. As it turns out, all these different games are the types that we love to play. I hope that shows through in the attention to detail and effort that has been put into making them fun, carefully balanced games that are easy to get into yet reward extended play - they are actually whole games in their own right, so to call them "minigames" does them a disservice, I think.
The other aspect of such a busy park and varied experience is that we really wanted you, the player, to be the one in control of what you actually did in the park - not the game forcing you to do stuff you don't want to. So Thrillville is very non-linear: you are never "on rails," and it's really down to you what you do at any given time. This means that people who may prefer dance games or flirting with the guests can progress just as well through the game as those who like first-person shooters or driving.
Keeping things non-linear but also maintaining a tangible story is a true challenge, and I'd have to say that the glue that keeps the game together lies within the mission structure. Grouped into different types, you only need to complete a certain proportion of them (of any type) to progress to the next park. So you can hang out in your park, doing exactly what you like to do - just like a real theme park.