Skeuomorphism
ITT: People talking about a design tool they didn't know existed 2 years ago.
All kidding aside, though, while I like the idea of less visual clutter, some gradients and shading are nice, especially on a desktop computer where a non-gradient, pure white background can wreak havoc on the eyes with a 27" monitor.
Skeuomorphism, in and of itself, isn't bad a thing. It's only when it exists with no functional purpose. Think of the "files" and "folders" in your computer's HDD. These are a skeuomorphic concept, and surely a justified use of it!
The dark texture on the Mavericks Reminders app is not bad; in fact it's similar to the background texture on the iOS7 Notes app. I don't find it distracting or distasteful, whatsoever. The notepad section of Reminders is, in fact, skeuomorphic, but it serves a functional purpose. The rule lines separate reminders and the margin provides a place for checkoffs. Unlike Game Center and Find My Friends, the Reminders app is an example skeumorphism done properly.
That said, I wouldn't be surprised if Reminders does eventually get a overhaul to fall in line with the new, simpler, flat, aesthetic Apple is going for, but I don't agree with the criticism directed at the current version.