As long ago as around 2001, with ActionScript 1 or 2, I was already building smart drag-and-drop calendar applications, where conference attendees could book all their sessions online in an easy-to-use and intuitive interface, that included tips, and complex hover states, with extra information at user's fingertips.
I'd say web-apps are almost getting to the same state of sophistication and user-friendliness around about now.
After that, with ActionScript 3, I was building interactive and immersive promo sites where users could explore alternative environments, build their own 3D worlds, or do crazy stuff like mash-up their own facial features (captured through their webcam) together with different celebrity musician's faces, and then do a remix of the musician's music (for an 'art' event that the musicians were taking part in).
There were masses of other capabilities - both serious and playful - but I must admit, even though I'm sometimes sad we lost Flash, in the end - especially when it was obvious that Adobe had let it drift - it was a shitshow of insecurity and bandwidth-waste.