I was never a Flash developer, but I certainly admired it in its prime. The early versions could be installed simply by putting a 47kb DLL in the plugins directory, and in a time well before the HTML canvas or JavaScript with good performance, this brought dead web pages to life in a way that was very portable across browsers and operating systems. It was much better (lighter, simpler, quicker to load) than Java applets from the mid 90s.
It's easy to imagine the various security vulnerabilities could have been fixed by a more responsible/responsive company, and the abuse by advertisement companies should've been solvable with an ad blocker.
JavaScript, CSS, and HTML have come a long way in capability, but the mashup is much more distasteful to me. Flash was elegant despite its frequent misuse.