Windows has come in many versions over the years - some better than others. Many of us just tolerate Windows at best but Windows 7 might change that. If you have a fairly new computer that runs Windows you NEED Windows 7 - it really is better. If you are running Vista now then do everything you can to upgrade to Windows 7 ASAP!
Windows 7 is really very similar to older versions of Windows but is clearly more polished and just seems to have fewer issues than previous releases. One very different feature would be the lack of a built in Email client. You must download Windows Live during the install. This is fine as the software is really not bad. While you are downloading be sure to get Microsoft Security Essentials as this is really a fine anti-virus package and is FREE!