I don't think it was so much the hype, as it was the TONE of the hype.
This was never "Goodfellas" or even remotely Scorsese-like. It was a straight up farce starring a squad of total morons who all think they're smarter than they really are. If anything, it felt more like a Coen Bros movie. Except there was an unearned happy ending for Bale/Adams.
But the worst thing that happened to American Hustle was an ad campaign that never really hinted at the idea the film is a big dumb comedy first and foremost. There are maybe one or two moments that are played straight total (Lawrence in the Bathroom, Renner kicking Bale out of his house) Everything else is watching entertainingly stupid people fuck themselves over, and laughing at their expense.