I worked there briefly in 2003, as part of the opening crew for Six Flags after they acquired the park from Jazzland's investment group. I was a Ride Supervisor, in charge of several attractions. But truth be told, I didn't last long. I was supposedly hired for my expertise, having been in attractions at WDW and Universal for a number of years, but no one would listen to me. I was rather appalled at Six Flags' policies and procedures on everything from guest service to basic ride safety. Of course, it didn't help that most of my staff consisted of kids from the neighborhood who didn't have the foggiest idea how or why they should greet a guest or check a seat belt.

I suggested a week-long training camp on basic customer service and safety issues (the opening crew was assembled at least a month before opening), but the company didn't want to spend the money. So I walked away from the whole mess.
I say that not to bag on Six Flags, but to give some idea of where the park was at even before Katrina. As others mentioned, it was located in troubled New Orleans East, in a high crime area far from the tourist district...and New Orleans East IS in the 9th Ward. The park's in the Upper 9, not the Lower 9 that got so much press. But anyway, not a good location from the start. I lived in the French Quarter and, like most Quarter residents at the time, didn't have a car. So I had to take the city bus, which was okay except for the bus change in a bad neighborhood.
Anyway, I think Jazzland was originally meant to be a mostly-locals park to hopefully revitalize some of New Orleans East. But of course, if the locals don't have money to go, then the only way to make money is to attract visitors. Supposedly Jazzland's problem was that they didn't have marketing funds. So Six Flags bought the place out and launched a huge marketing campaign, but of course that didn't overcome the original problems.
The entire neighborhood took over 20 feet of water in the storm. We went back three weeks after Katrina to take care of some personal matters, and we drove out as far as we could in that direction to try to see the park. We couldn't get very close, as everything was STILL submerged. It took over a month to drain the water.
What was really sad, though, was what happened after the city reopened. Over 70% of the housing stock was heavily damaged or destroyed. In New Orleans East, there was almost NOTHING left. So FEMA sent up trailer villages all over town. One was located literally in the parking lot of Six Flags. Can you imagine being a 5 year old kid, having lost everything, having to wake up every morning and SEE all those rides, but not being able to go on them?
We drove down there when we were back in 2007, but never got brave enough to go inside and look around. Just from the street, though, it was easy to see that the place was just destroyed. Of course there's graffiti and vandalism, it's an attractive nuisance. But it was beyond hope before all that. Rides just aren't meant to be submerged in standing water for weeks on end.
With the problems that the park was already having, there was no way Six Flags was going to go in and pay to rebuild it. The problem was, they had signed a 99-year lease. And with the city in dire straits, no one was too eager to let Six Flags out of the lease. So the property has sat empty and unmaintained while the battle raged between the park and the city.
Although I hear Six Flags is in some trouble now, because they allegedly went in and removed some salvageable property that wasn't really theirs--it had belonged to Jazzland--for use in other parks. Supposedly it was in the contract that they could USE whatever had been there, but they couldn't remove it. That's all hearsay, so take it with a grain of salt.
But there you have it, the saga of Six Flags New Orleans.