1) If you use Mission Control, there's a linen background hidden behind the desktop. If you open the Notification Center, there's a linen background hidden behind the desktop. But if you change desktop spaces, there's only black - where's the linen (i.e. what happened to that permament physical textured backdrop Apple apparently decided was the bedrock of the UI?)

2) Not to mention that gross effect when you change desktop spaces, and the whole desktop slides over - including the menu bar (that apparently static, foundational part of the UI) - to be replace by a new menu bar! The dock doesn't change, so why does the menu bar?

3) And of course that other gross effect when you click full screen on an app (that little full-screen button nestled oddly in the top right corner of the window chrome above all the other little static buttons) - and the whole thing morphs and bulges and slides into a new space. Yeesh.

4) And yeah, Launchpad. So now apps are scattered between the dock, the application folder, and the Launchpad. Great.

5) Also, the Finder seems to get worse with every generation.

Really though, it's the sum of all the parts that offends me. When I see people with their sleek Macbook Airs on their laps, then I look at their screens, and I see stacks and stacks of scattered windows of all shapes and sizing clustered over the desktop, and everywhere, fiddly little tiny click targets (in the menu bar, in the windows themselves, in the window chrome - don't get me started on those ghastly mini traffic light buttons for mini windows...) And they're moving their fingers around in that little touchpad controlling that little mouse pointer on the screen, tapping on the little targets or slowly dragging things around...

All of this stuff was fine when computers were big slow things that sat on desks, running a handful of low-res apps at a time, driven by a mouse and keyboard. Back then, it wasn't possible to implement the fast, fluid, colourful graphical design and interface features of Metro. Windows had to be static heavy things that you carefully dragged around, resizing individual edges one mouse drag at a time. Nothing had any momentum, the whole window stack just sort of sat there like a pile of lead sheets. But now that computers are in our laps, or in our hands, and our computer use is spread between multiple device, and more often than not the average person is using a touchpad or a touchscreen to browse the internet (which has expanded into something so huge it no longer makes any sense to bottle it up in a single browser window) - and especially now that touchscreens are about to become ubiquitous on every single laptop sold in the world - the old static clunky WIMP model needs to be shuffled off to the side in place of something that makes more sense.

I will note that Mountain Lion isn't qualitatively worse for this new stage of computing than, say, Windows 7. But I have no respect for the small attempts to modernise the OS with ported iOS features. It's putting lipstick on a pig (admittedly a pig that was very good and useful for a long time and still has a lot of value in many different contexts.) Microsoft's hard reset will ultimately produce the right OS for the times, Apple's slow tweaks won't. In my opinion at least.