The tooling was amazing. I used to do a ton of Flash development back in the day, and the ability to seamlessly create the UI and backend code is still light ye

The tooling was amazing. I used to do a ton of Flash development back in the day, and the ability to seamlessly create the UI and backend code is still light years ahead of the cross-browser nightmare of creating HTML5 apps. I think Adobe has tried to achieve the same level of functionality with other tools over the years (Adobe Edge Suite), but it never really made it to the same level as web application development in Flash.