I was a Flash aficionado back in the early 2000s. Back then it was a good way to get something moving on your page or to provide a bit of interactivity. HTML 5 was some way off, iFrames were clunky, and JavaScript libraries like jQuery weren't very mature yet. Plus the player had a small footprint and was pretty widely installed on the browsers of the time. For a time it was a great way to deliver video.
As a technology it was a decent stopgap measure IMHO but it was on borrowed time as open standards caught up. Not many slashdotters had anything positive to say about it because it was a closed standard, but I have fond memories of seeing what the future of the web looked like, even if it was implemented in a doomed technology.