The Advantages of HTML5

Simpler syntax
such as <!DOCTYPE html> and <html> tags
Semantic tags
These tags describe the content (instead of formatting it) and also can use for grouping and formatting same contents simultaneously
<nav> , <header> , <section> , <footer> , <article> and <aside> for dividing and sectioning of page. These tags are used in the same way as <div> tag
<hgroup> for grouping <h> tags
<figure> and <figurecaption> for grouping <img> tags
Simpler and more efficient Multimedia
<audio> and <video> tags instead of old <embed> and <object> tags
<canvas> tag for more creative and beautiful graphics and animations
Deleting some old tags
<font> tag: <span> tag with styles (CSS) are used instead
<frame> and <frameset> tags
New form controls and properties
Input controls for getting email and urls: <input type="email"> and <input type="url">
Input control with Placeholder property: <input type="text" placeholder="text ...">
Spin box control for getting increasing or decreasing numbers: <input type="number">
Slider control for selecting a number from a range by mouse: <input type="range">
Date picker control for selecting date and time: <input type="date">
More use of Javascript, CSS, Javascript libraries (like JQuery), and AJAX technology