This is a huge can of worms, but I think @sdw put it best:
“Very 'flat' UI is a meaningless reactionary design fad vs. overdesigned UI. Good designers aren't limited by style but taste and discretion.” twitter.com
We should strive to build the best possible app to solve the particular problem we’re trying to solve, not to follow a specific style or meet some arbitrary idea of good taste. Some aspects of what is labeled skeuomorphism actually aid in usability. @gruber generally did a good job walking the fine line between matters of taste and matters of usability, but that nuance seems to be lost on many people.
An app that uses leather textures and nails usability is better for the user than a convoluted app with no texture.