What it looks like Microsoft is doing is having the casual/fun/afterhours stuff appear on the desktop when booting is finished. Then if you need to do serious computing stuff, you hit the desktop tile which takes you to the regular desktop Windows.
Actually, I see nothing wrong with this approach especially if the Metro apps gets better, and of course there are more of them. Metro apps look very nice and can take advantage of larger screens. For me, Metro even works fine with a mouse.
Once you get done with the simple apps and need to get work done, you can go to the desktop and pretty much stay there if you like. Worrying now about the lack of a Start Menu is needless in my opinion. I expect there will be 3rd parties that will bring something close to the old Start Menu.
Even if they do not, you can create you own application launcher by just creating a new toolbar onto your taskbar and adding whatever shortcuts and/or folders you want. Somebody should just create a program that does this for you. It would be easy too since all you need to do is create folders and shortcuts.
If Metro made Window 8 much slower compared to 7, then that would be a legitimate complaint. I am waiting to see final benchmarks, but it seems like 8 roughly equal or better than 7. I already know that 8 took only a few minutes to install and boots quickly.
So to me right now, there are no deal-breakers as far as using Windows 8 is concerned. Of course, I will have to wait until RTM to see if about bugs or compatibility issues.