Gary appears to be on the rebound. Looks like they're tearing a lot of that stuff down, and building new stuff.
Detroit has plenty of cool abandonment, as well. Lots of good pictures coming out of there.
As I understand it, Gary was a company town. It's not surprising that a city built solely for the employees of one company should disintegrate once that company collapses. Furthermore, I don't believe that unions were their downfall. Massive imports of cheap foreign steel is what did them in.