The new Metro Style Apps and traditional Windows applications differ in a number of ways. Some of them are explained below:
New Metro Style Apps have a different look and user experience. They have borderless windows, with no option to resize or close. To close a Metro App, all you have to do is swipe from top to bottom or switch over to another app. The traditional Windows program have minimize, maximize, resize and close options.
Metro Apps are optimized for touch operations but can work well with other types of inputs like keyboard, mouse etc as well. Regular Windows programs works best with mouse and keyboard.
Metro Apps can interact with user and provide notifications or updates to users through the Tile even when it is not running. In case of traditional Windows programs, when it is closed, it is completely removed from the process space and it cannot interact or respond to users.
Metro Style Apps have access to a new set of Windows APIs that allow it to interact with various new Windows 8 commands and functions like Charms bar, App bar etc.
Metro Apps do not have access to all the system APIs for security reasons.
Traditional Windows programs can be developed and distributed by developers or product companies. But the Metro Apps can be distributed through Windows App Store only. This would mean users can depend on the trust level of the seller at the App store. It gives a unified platform for end-users to compare, evaluate and purchase the best App for them.
The primary difference between Metro Style App and traditional Windows programs is, the Metro Apps are designed for touch based devices and traditional Windows programs are meant for desktops and laptops that uses keyboard and mouse as primary input devices.
Considering the way Microsoft is pushing Touch based features and apps, the computer industry may lean towards touch sensitive screens for all types of computers including desktops and laptops. This could lead to massive popularity of Metro Apps over traditional Windows 8 in the next couple of years.