If you like designing things and tweaking them to make them better... and you've ever been intrigued by the marketing and wizardry behind a large theme park, then you'll LOVE
Sim Theme Park (apparently also known as 'Theme Park World,' according to the intro). The familiar cause/effect tweaking is in full effect in this title, allowing you to determine everything from the price of admission to the amount of ice in the drinks. One of the most entertaining features is the ability to create your own roller coaster and then actually simulate riding it first person. The graphics may be less than spectacular, but if you design your coaster right, you can actually get that 'motion' feeling just by watching the screen. Cool.
You definitely have to have patience to play Sim Theme Park, as with pretty much any Sim title. But this game is a blast to play.