HTML5 is an extended version of HTML and it is still considered in its experimental stage since lots of browsers don't have much support on it. It is still worth messy with though just so you can get an idea of it.
Here are some benefits and difference of HTML5:
HTML5 is supposedly know to improve site accessibilityfor two main reasons: semantics and ARIA. HTML headings like <header>, <footer>, <nav>, <section>, <aside>, etc. allow screen readers to easily access content.
HTML5 uses different tags and method for video/audio. More supportive for mobile devices that don't support flash.
You can say it also gives cleaner code due to its semantics. But, older browsers and IE (of course) don't support that new code.
HTML5 (mixed with other scripting) has a local storage feature. It’s similar to a cross between regular old cookies and a client-side database. But since it allows for storage across multiple windows, it has better security and performance and data will persist even after the browser is closed. This storage feature allows web apps possible without the need of third party plugins. Being able to store data in the user’s browser allows you to easily create those app features like: storing user information, the ability to cache data, and the ability to load the user’s previous application state. Details can be found here: http://24ways.org/2010/html5-local-storage
HTML5 with Canvas allows for more types of interaction and animations. It suppose to also be great for game development
Last edited by Puddlemut; 09-27-2012 at 11:56 AM..