Release of HTML 5 marks the new age of web design and development. Previous standard, HTML 4, released in 1999, was lagging behind modern design trends for years. Thanks to that every developer had their own implementations of typical user interface elements. Naturally, that divided the web and users, as it was prohibitively expensive to support every possible platform.
Besides purely development advantages (less technologies and languages to learn), there are also benefits for the average user. Video and audio content is now naturally supported by browsers, which means media content can be consumed identically on any platform, be it PC, or gaming console, or mobile phone. General cross-browser compatibility is also much better today, than it ever was, with similar experience between desktop and mobile.
Did you know that this website is also using HTML 5?