Key Features
Zero external configuration per page/action (ActionBeans are auto-discovered, and configured using annotations)
Powerful binding engine that will build complex object webs out of the request parameters
Easy to use (and localized) validation and type conversion system
Localization system that works even when you use direct JSP->JSP links
Ability to re-use ActionBeans as view helpers
Ridiculously easy to use indexed property support
Built in support for multiple events per form
Transparent file upload capabilities
Support for incremental development (e.g. you can build and test your JSP before even thinking about your ActionBean)
And a lot of built in flexibility that you only have to be aware of when you need to use it