The flat UI trend has been rampant, much like the functional achitecture trend many decades ago. Would you like it to continue?
I make my judgements on UIs based on actual implementation and usability.
I like KDE 5's implementation of flat UI not enough to use it though. I hope the flat fad is exactly that and we can go back to "normal" UI's soonish.
To me, it's not so much the "flatness" as the consistency of the UI. Currently in iOS, buttons change location and look depending on the app and the device. I'm not a big fan of plain text as a button, but the least they could do is put the delete button (for example) in the same spot from app to app. Sometimes it's on top, sometimes the bottom. Sometimes it's text and sometimes it's a little trash can icon. It all seems haphazard.
And for the love of God, fix the nauseating color choices! Will someone please tell Jony Ive that yellow text on a white background is nearly illegible!
I'm not a fan of the flat UI design. I liked skeuomorphic design of iOS 6 and earlier OSX.