I never understood why there was this big sudden push to kill Flash. HTML5 is fine for playing videos, but for a lot of the artistic uses of Flash, it's no replacement at all, and there are no other good replacements either. My job involves building and managing websites, and it's painfully obvious that creativity has taken a step backwards in several areas because even if Flash is the only thing capable of doing a task, no one wants to use it.
One site I built a while back used to have an interactive map created in Flash, and when it was time to redesign it, the so-called "experts" insisted that we could do it just as well using Google Maps ... I was skeptical but went along with it. Well guess what, the Google Maps version was nothing like it and it sucked. "This is crap," I said, "what are our other options?" "There are no other options, you can't use Flash because of Apple, so this is it," they said. I told them I didn't care about Apple users, who made up about 2.75% of our audience, enough to design the whole site around them, but was shouted down. Garbage.
There was never anything wrong with Flash; it was as vulnerable and glitchy as any other widely used plugin, and the positives far outweighed any of that. As others have said, the campaign against it was all because of Steve Jobs (may he burn in hell) and his insistence on being a control freak. It's a shame so many people were dumb enough to fall for it.
*no, I'm not wishing Steve Jobs to burn in hell over Flash; that would be silly. He was just a jerk with a horrible mentality.