What are some high level improvements over 4.9 that would make someone want to upgrade from 4.9 to 5, or even select 5.0 when installing a new site rather than 4.9?

I realize a lot of hard work went into the new codebase, but sifting through thousands of items on the support site is too granular.  Can someone give me the executive summary as to why 5.x is better than the 4.x  codebase?

Thanks in advance

Major Highlights for 5.0.0/1 as taken from Codeplex: 

• Added jQuery support to the core platform. jQuery will now be distributed as part of the DotNetNuke installation and will be available for use by module developers.
• Added support for Internet Explorer 8 Web Slices. Administrators can configure any module to use IE8 Web Slices including the ability to set time-to-live and expiration values.
• Removed distinction between admin modules and pages and normal pages. This allows administrators to easily delegate access to any portion of the application to any group of users.
• Updated the installation services to support manifest files for all extension types. Now skins, containers, providers and modules are all first class citizens that can be installed and uninstalled.
• Expanded XHTML, WCAG and ADA compliance.
• Refactored core to improve support for Unit Testing. Refactored several core classes to use interfaces and added a simple component factory to provide dependency injection support.
• Added ability to deny permissions in the permissions grid. This new feature extends the permission framework to give administrators greater flexibility in defining permissions.
• Added Widget framework. The new Widget framework allows you to quickly add JavaScript/html widgets to your site with very little effort. The framework supports the use of a simple object tag based representation which means you don’t have to know JavaScript in order to add the widgets.
• Added new Object notation for using skin objects in Skins. Skin designers will no longer need to include separate XML files when creating and packaging skins. No more funky “SKINOBJECT” tags littering your html. This significantly simplifies the process of creating skins and further opens up skin development to a broader group of designers. If you include a simple JavaScript reference in your HTML skin, you can even get a full WYSIWYG experience when designing your skin.
• Added the ability to automatically update user roles without requiring the user to logout and log back in.
• Changed the user deletion code to use a soft-delete rather than removing the user record. This ensures that modules like the Forums behave correctly for a previously "deleted" user.
• Added IP logging to the User's table to capture the last IP address from which a user logged in.