Microsoft has hardly ever completly rebuilt an OS, 95 and 98 are essentially the same at the core, just a few changes to make the latter better, Windows XP was based on 2000 and NT at the core, even Windows 7 is based on Vista (alot of changes for stability etc), Windows 7 is Vista 2.0, but they needed to rebrand it, because of the tarnished reputation of Vista.
Also what you are saying is we HAVE to buy something that looks like it was made by a 5 year old to use it properly, that Arc touch mouse is the uglyest thing I have seen, it does not look comfortable to use, and looks like it will suck for games.
Seriously, the metro UI is made for tablets and phones, I will hate using it hated everything to do with metro with a mouse and touchpad (multi-touch)
Microsoft WILL loose people by forcing them to use metro, the (what they call it) Legacy start menu is ideal, everything is there, in a logical order (alphabetical) whereas on metro they are in the order you install them, it will be a nightmare finding things among hundreds of apps and programs, they can't even make the tiles the same size, some have large ones others have small ones, it looks ugly. I will be downloading the release preview, and probably beta if I can get hold of it to try out (alot has changed since developer preview) but my expectations are extremely low after what I saw in the developer preview.
I believe Windows 8 will fail badly (looking at ME style failure) on PCs and laptops, Metro will however work on phones and tablets, Microsoft could have done one thing, have metro enabled by default, but add the classic desktop and start menu as an option, alot will use metro because they stick with defaults, people who really cared about it will switch, or if they like it even stick with metro, this is the wonderful thing about linux, you don't like one thing, change it.