Unfortunately, this isn't really all that surprising. The economic meltdown of 2008 brought a massive drop in disposable income, which has led to falling amusement park revenues. While Disney, the undisputed king of the hill, has been cutting employees and imposing other austerity measures, lesser lights have been going out of business.
As the Theme Park Insider noted almost two years ago, Six Flags' downfall has been a long time coming. Initially beset by the fact that their properties were overvalued in the real estate bubble, the company has subsequently been undermined by the dwindling finances of its customers and its own stock problems.
The company's biggest worry is its looming debt. It has until August 15 to pay $287.5 million to holders of its "preferred income equity redeemable shares." With additional costs added in, Six Flags' liability may be as much as $315 million. With credit frozen and its own prospects bleak, it seems unlikely that the company will be able to make that deadline.