After a few hours with it, though I am still setting it up... I don't see what ALL the hate is about. Some hate, sure... but it is certainly not as bad as Vista was since its actually a bit faster than Win 7 and can use Win 7 drivers so hardware compatibility isn't that big a deal. The hate is really all about the UI and of course the writing on the wall about where the OS is going.
The main problem I see is that it is really 2 OSes cobbled into one. And MS did not do a good job explaining the differences.
The start menu is replaced by the tiles interface and Windows RT OS UI (ie. the tablet OS, ie. the Xbox360 UI)
However there is a desktop tile. Hit that and you are basically back in Win7 OS land, minus the start menu. In its place is an icon that takes you back to tiles. You can right click it and get a very handy menu though. I think you can even default Win8 to logging right into the desktop tile somehow so you never have to see the tiles if you don't want to. If anyone knows how to do this, I would be glad to know.
The other big stumbling block is understanding the difference between Apps (capital A apps) and desktop applications aka legacy apps.
Starting with the desktop, its the same Win7 desktop we all know and love. It is traditional multitasking and multi-threaded and does its thing with desktop programs, services, steams games, etc. but there are also capital A Apps. I think of them like the old widgets. They also run and you can switch from them and the desktop pretty easily, however it is here were the UI interaction falls down a bit, at least with a mouse and keyboard.
The Apps and the tiles basically live in the foreground.... they really have no interaction with the desktop, can't be pinned to the desktop taskbar or the desktop itself or alter it in any way. They can be pinned as a tile and the start bar but that acts an overlay to the desktop. Its like the desktop runs as an app itself. Its the interaction between desktop and Metro that feels odd, probably perfectly natural with a touch screen but kludgey with a mouse. For example to close a Metro app is cumbersome with keyboard and mouse. I'd naturally X it or right-click close but instead you have to select the top of it and pull it down, mimicing the touch gesture. At least it can also be closed by starting taskman and ending task, so that is not that bad but an x in the corner when mousing over the top right would have went a long way for mouse users.
Likewise desktop apps can't interact with live tiles either, save the desktop tile, which shows a thumbnail of your desktop, though it isn't "Live" but a thumbnail of your background. You can use and see the Apps as an overlay on the desktop (think hitting shift-tab while in a game running through steam, you get the overlay where you can do some things... only this includes launching a mail app, netflix, etc. The sky is the limit depending on whats in the app store). This is neat. Especially since you can pin a metro app, such as netflix to the side as 1/3rd of the screen, and pin the desktop to the other 2/3rds... work and watch netflix on one screen. ;-) Not sure how this would work multi-monitor but that is neat. It seems like it would lend itself well, but it all comes down to how MS handled it (I don't use multimonitor so...)
However they really did gimp it in an important way. It would be much better if you could have desktops apps create a live tile or RT apps interact more with the desktop. However, desktop apps aren't curated via the app store and they have the arbitrary restriction of no desktop apps with live tiles. I think they really missed an opportunity here (or artificially created another one depending on how you look at it.).
Otherwise, so far so good. Im giving it a qualified nice BUT no reason to upgrade from 7 if you are happy with your current functionality.
I didn't touch on storage pooling, etc. and a few other nuts and bolts that make it nice as a home server (which is my intended use). That and acting as my HTPC frontend with the eventual media Metro apps (such as Netflix and Hulu) combined with desktop XBMC make it a nice upgrade over Win7 I think.
However, the one app I tried extensively, other than the Mail app (linked to my hotmail account) was Netflix. The Netflix app is hardware accelerated so would allow HD playback on an Atom ION or E350 box. Nice for people with small settop HTPCs. This is an upgrade over their regular PC interface via the website and silverlight. However its UI as designed requires a mouse for some functionality and is optimized for touch. It is a snazzy app but its not meant to be used with a PC I think. That is not MS' fault, its lazy Netflix app makers not making it work with just the keyboard. It would be even better if it could use the MCE remote. The UI of the app itself would lend itself to a 10' UI but with no practical way to interact with that UI its useless at 10'. The MCE Remote works fine in XBMC in Win8 desktop but I am not sure if the MCE Remote can interact with Windows RT apps, it does work for selecting between tiles, so it might be allowed, I am not sure of the Metro app UX requirements. Only bonus would be DD/DD+ 5.1 output support, its currently stereo only (which corresponds to its tablet oriented use). I hope we see more apps designed with remote and 10' UI in mind but it is still early.