A friend of mine made this game and so far its pretty fun! Thrilltown was released this week so you can get to be competitive from the start...
http://www.thrilltown.com/register.php?r=64
Things you can do:
Manage Employees - hire workers, train them, and designate tasks
Build attrations like bumper cars and roller coasters and upgrade them to awesomeness
Market to your park-goers and appealing your parks specialties to their tastes.
Build kiosks and game shops
Manage ticket prices, shop prices, ride prices.
Expand your park and your bank
Socialize and become the best!
Join my corporation as we begin to crush our competition!
http://www.thrilltown.com/register.php?r=64
Also there are options for premium membership to gain access to bonuses and perks. I've bought the corporation perk that reduces the costs of all rides you build in your park.