I see W8 as a reaction to a new world of computing: more powerful computers, a proliferation of device formats, ubiquitous connectivity, a dissolving desktop-cloud barrier, pervasive social/identity services, mass-consumer computing, mostly for a whole emerging range of novel, non-traditional computer tasks. 

The WIMP desktop is a legacy product from the days of computers as workstations and computer-users as skilled specialists. The desktop is very static and rigid. Windows only move when clicked and dragged, only change size when their edges are pulled. The desktop can become as cluttered as you want with multiple windows and desktop folders and icons. This made sense in 1995, but now computers are far more powerful, and graphical display techniques are better too. W8 is fluid and dynamic where WIMP is sluggish and static. Tap or click on a tile and a whole new screen flips up, filling the screen. Even compared to iOS, Metro is far more dynamic, mainly due to its radically simpler design language. The basic fonts and block colours of Metro can squish and stretch and dynamically resize in a way which is largely impossible with the carefully detailed chrome of iOS.

This fluidity also extends to the way the tasks flow into one another in the OS. Talking mostly from my experience with WP7, it’s remarkable how wall-less the OS can be. The way you can move from a messaging thread to your messagee’s contact card, simply by tapping their name, and seeing all their latest social activity on Facebook, is great. Ideally, Metro is wall-less - the opposite of iOS’s carefully segregated app ghettos. The platonic Metro ideal is that all the parts of the OS flow seamlessly together (it remains to be seen how successfully Microsoft can pull this off - also this quite different model may be difficult for developers used to iOS to get their heads around and take full advantage of).

Furthermore, visually the Metro frontend is clearly the cleanest and simplest consumer OS ever. It's a massive decluttering effort to display only relevant info, and much much easier to understand than any previous OS. And Microsoft is aiming to make this design language uniform across phones, tablets and PCs, and their web presence. It has the most common net identity services baked in - and the whole platform is tied together with Windows ID, and all your files and info synced seamlessly across all of your Windows devices with Skydrive. So, for example, if I made an account on a W8 PC, it would prepare all of my contacts from Facebook and my calendar appointments because it knows me from my Windows phone. The aim as I understand it is radical flexibility - you can shift seamlessly from device to device and the environment is consistent throughout - it just works. Also part of the idea with Metro is to dissolve the web/desktop barrier - instead of just accessing web services through a browser and some dedicated programs (IM, torrent clients etc) and perhaps some desktop widgets, the web is baked in to the skeleton of the OS. Which makes sense.

Not sure if I'm explaining this well... As I said, it remains to be seen whether Microsoft makes good on this potential. I’m just trying to articulate what I think Metro represents, what I sense is possible here. And trying to do so without just sounding like Microsoft PR :)

It seems like maybe a lot of people are offended by W8 because it's too simple and potentially interferes with the quite complex workflows I assume average HN readers do with their computers. But for the average user, I think W8 is going to be great. Computers need to be democratised further - right now, the vast majority have almost no idea how to use WIMP. It’s just too complex. OS X is just as bad - in some ways even worse than W7! The value of W8 will be through hiding 95% of the compexity of computers from the average user, while preserving the technical backend for more advanced users. Normal users get a massively more approachable experience, allowing them to think less and spend more time doing the stuff they really want to with their computers. Advanced users can still go deeper (unlike Apple, which seems intent on locking down their entire system at the expense of advanced desktop users - and without giving any real gains in useability to justify it!)

People forget, I think, that Microsoft focuses a lot on useability. Metro is the result of a lot of hard work thinking how to make computers more useable. Apple focuses on products that wow people. But from my experience with the iPad, it seems Apple thinks less about useability than people might expect (non-resizable thumb keyboard, I’m looking at you...)

I think W8 is best seen as a transition product, making the first steps away from the old WIMP desktop. So yeah, right now, they haven't tinkered with the old desktop much. But a split is forming: between the simple easy-to-use frontend of the OS and the technical backend. Expect this split to become more coherent in W9.