Currently METRO can't be disabled at all by any set of included default options in the current preview builds, but I'm guessing this is to encourage people to explore METRO during the preview since it wouldn't really take much to put the more regular start menu in any sort of final release.

Choice

That's all Windows has ever done with masses of choices for interface interaction which you never find in OSX, but you know what people do? They chose to stick to what they know and then later complain about it to say windows is just boring and never changes. Then when Apple implements something it's unquestioningly accepted as "gorgeous" by all its fans to then be desired by all who don't have Macs too for windows to then get sand kicked in their faces for being a lame OS for suites and business bods only. Such is the world. The strange thing is much of the basic navigational features that OSX has in terms of layout can actually be contextually applied in Windows through default menu options without using patches or tweaks. (minus the thinger, although there is a highly polished third party solution for that too). 

I look at the METRO Start page as being a bit like the full screen Launchpad in OSX Mountain lion. Where as the Launchpad only shows icon to launch apps the Start page allows you to pin feeds and informational tiles too for quickly glancing over. The start page also allows you to instantly drop back onto the desktop we all recognize with Aero taskbar simply by clicking an icon on the star page that shows a representation of the desktop.  Yes the desktop is still there with an Aero taskbar that you can still pin Apps too, only it no longer has a start button on it. 

Toolbars (even less reason to go into METRO in 8 if you don't want to)

 
 
The ability to add "toolbars" to the main Aero task bar has been with us pre XP (if I remember correctly it was in Windows 95 too, although obviously we didn't have Aero back then). You can either add predefined toolbars or custom toolbars which will display the contents of an entire folder of your choice like a drop down menu from the taskbar itself! Need to have a drop down menu for a particular group of apps? Just create a folder with the shortcuts for your chosen grouped apps in them then assign that folder as a toolbar on the taskbar, et voila an instant custom quick access drop down menu directly from the task bar. Alternately you could also just pin your apps directly to the task bar too.  


 
There's a default pre-defined toolbar that you can add to the taskbar called "desktop". You can add this by right clicking the taskbar for a drop down menu to appear. From the drop down menu click "toolbars" and then "desktop". The word "desktop" should now appear on your taskbar. click it with open a quick access drop down menu or alternately you can double click it to expand the toolbar. double clicking it again will collapse the toolbar. Within the desktop toolbar you can quickly access open up a window to all your user folders/libraries for the documents, pictures, music and videos folders, a bit like in OSX.

You can also place this toolbar anywhere you like on the taskbar.


 
Desktop icons (another reason to not go into METRO in 8 if you don't want to)

It's also still perfectly possible to create desktop icons for apps and desktop folders to store files in if you don't want to use toolbars directly from the taskbar.  

Personally I actually quite like METRO even on my none multi-touch laptop, and even though its not quite finished in the current preview build. 




Close your eyes. Think for a moment... do you really ever often go into the "all programs" menu?


 
The odd thing is when truly thinking about it I never have much reason to go into the "All programs" menu.  Anything I do use I pin directly to the taskbar or launch from last used programs directly available from the start menu pop out. I sometimes also pin stuff to that for quick access too. The Metro Start page is like a flashier full screen version of that which allows you pin other stuff to it then just your most commonly used apps. How many people out there do actually frequently need to go into the "All programs" menu? Even then the equivalent to the  "all programs" menu is still accessible by right clicking on the METRO start page from which you can selectively pin your most commonly used apps to the full screen METRO start page or the main AERO taskbar on the main desktop.