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The Instagram redesign takes lots of cues from the Facebook redesign, which is expected. Maybe they wanted to unify the look of their apps?

I like Instagram's new look, even though it looks like they just flattened everything. It looks great on my iPad Mini, which can finally use the Retina assets inside iPhone-only apps.

I feel that apps should still have the creative license to deviate somewhat from the look of the OS. I wouldn't want every app to look like iOS 7's Mail or Safari.
 
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