The most noticeable change is those Live Tile feature on Windows 8 Start Screen, which provide access to some nice apps with just one muse click.

But due to some reason some people are not liking and want old classic Windows 7 like start menu back, if you too want this then here is an nice app for you.

Solo-Dev at DA has created Windows 8 Start Menu Toggle is an nice allows you to toggle between the Metro Start screen and the Classic start menu in Windows 8 Developer Preview.

Windows 8 Start Menu Toggle

This app is only for Windows 8, and you need to have .Net 3.5.1 runtimes, Run this tool As Administration.