“The web is constantly evolving. New and innovative websites are being created every day, pushing the boundaries of HTML in every direction. HTML 4 has been around for nearly a decade now, and publishers seeking new techniques to provide enhanced functionality are being held back by the constraints of the language and browsers.” Source: A List Apart
A List Apart gives us a short preview of what we might expect in HTML 5. There are interesting changes and news regarding structuring of WEB-pages as well as some new tags, such as media like video and audio. Embedding video in WEB-pages has been a nightmare; Firefox have no issues, of course, and Opera has often the same result. But Internet Explorer 6 and 7 has always been difficult. Even embedding a Microsoft product, such as Windows Media Player, in IE is not easy.
Anyways, enough crap about Microsoft. I actually like Microsoft…
Take a look at the complete article A Preview of HTML 5.