I'm still not convinced. Perhaps if he wasn't such a mockery of a...caricature, then it would be easier to digest, but in his current form, I honestly don't believe that him being mentally ill was an angle the film sought to explore. If it was, it certainly wasn't resolved in any sort of meaningful way.
Exactly. If you're going to go the "mentally disturbed" angle. Don't go for the most obvious, overblown, cartoonish portrayal possible. It ends up feeling extremely patronizing- like something meant for children, as opposed to a more intelligent nuanced portrayal that can appeal to adults as well (Even Pixar did it better with Syndrome in the Incredibles).
That said, I did feel that Foxx's portrayal/efforts brought a lot to the role and made me at least feel something for the character (I'm talking just barely here)