I've seen this site and this site, but that's a lot to digest. What are the main things about HTML5 that make it different/better than regular old (X)HTML/CSS?
What is new in HTML5/CSS3?
html5;css3;css;xhtml;html
HTML5 is huge, but also awesome.In my view, it is mostly about interoperability. The spec goes and specifies even edge cases to try and make sure that all browsers read the markup the same way.In second place, HTML5 has video and audio, which do exactly what the name says it does. If you want to include video or audio, HTML5 should reduce your plugin needs.In third place, HTML5 includes lots of accessibility and semantic help. For instance, elements like <section> and <article> help machines figure out what content is supposed to be. New input types like <input type=email> can also be useful for the same reasons, although the new input types include custom UIs which make them useful even for common human readers.Note that the new Forms features are much more than new input types. It also includes support for placeholder text and several other attributes.HTML5 includes <canvas>, which allows drawing 2D(and, with WebGL, 3D) shapes like charts or even render games.Old behavior is now standardized, such as Internet Explorer's ancient contentEditable.The DOCTYPE is finally decent! You can now actually memorize it! <!DOCTYPE html>Specifying encoding is also easier, with <meta charset=utf-8>.If you want to send data to the client and associate it with elements, you can now do it with custom attributes. For instance, <div data-status=open>Open</div> is now finally allowed. Note that custom attribute names must be prefixed with data-.You can now include SVG and MathML in HTML documents. Previously, you could only do it with XHTML documents.Among the multiple new functions and fields HTML5 defines, one of the most impressive is classList, which enables you to manipulate the class attribute more easily. Instead of having to getAttribute/setAttribute and use complex hacks to figure out which classes an element has and remove a specific class from that element, classList makes those hard situations very simple.There are also multiple related specs, such as Web Workers, Web Sockets and IndexedDB, which are not really part of HTML5 but everybody talks about them as if they were. They are very useful for taking advantage of multi-core computers, communicating with servers and storing data locally.As for CSS3, it includes support for animations, transitions, rounded borders and the flexible box model.Also new in CSS3 are the new selectors, which make it simpler to match specific elements on a page(such as only the odd or even rows in a table).Opacity, new units, marquee and ruby are also part of CSS3.I think that pretty much covers all important parts.