HTML 5 makes several improvements on the following traits, and more!
Semantics
Describe your HTML content more accurately (footer, header, nav)
Connectivity
Communicate with the server in different ways (XMLHttpRequest)
Storage
HTML local storage can replace cookies
Multimedia
Videos don't require plugins like flash, just use the 'video'
New elements allow better media implementations
Performance
Speed and hardware optimization
Device Compatibility
Various devices can load webpages uniquely
Loads of great examples on W3Schools!
Here are some that everyone might find useful:
You can reference W3 schools for more information on HTML5: here