A few days into learning Symfony and so far I'm keen on

• configuration check to start with
• good MVC separation
• ability to generate initial MVC components from a database definition
• form validation to match database constraints
• wrapping various HTTP functions and globals in a request and response object
• separate dev and prod environments
• ajax integration - like defining a div as draggable in PHP
• explicit support for initial and test data

Things not to like