HTML5 introduced new form elements, attributes, and input types to improve the user experience of web forms. Key additions included the <datalist> element for autocomplete suggestions, <keygen> for digital signatures, and <output> to display calculation results. HTML5 also defined new input types like email, url, tel, and color to provide native form validation for specific data types. While browser support for HTML5 forms has increased, some features remain incompatible with older browsers, so backward compatibility must still be considered.