The problem is mainly the lack of visual cues; there is no way to tell that sliding the main screen to the left will toggle the alarm on in Rise, or pinching a list in Clear will minimize it and take you up a level in the hierarchy. It’s not obvious, and what’s often called mystery meat.
Clear is beautiful, but it’s hard to argue that it’s well-designed in light of its mystery interface. It’s important to remember what Sacha Greif said yesterday:
… it’s important to ask ourselves if we’re embracing flat design because it’s a better solution to whatever problem we happen to be solving, or if we’re just trying to be different (and ending up being just the same as all the other people who are trying to be different too).
In many cases, I’m seeing the flat aesthetic used because gloss is just so 2008, without recognizing its ease-of-use shortcomings. Current (and future) UI problems are not gloss vs. flat — they’re something much more nuanced.