Flash was fun but it was never built for being responsive and handling desktop and mobile in one app. Everything was basically fixed layout. Adding in that responsiveness would have probably killed the "easy" part.
Although Flash really sucked as a technology, it did inspire a lot of visual artistry on the web. Half of the cool stuff you saw on StumbleUpon was made with Flash by people who weren't proficient with JS/CSS, which weren’t capable enough to achieve the same results anyway.
Good riddance. I once had the honor of being featured together with many other artist on an HP website. It was implemented in Flash though, meaning it existed as a smallish rectangle in the middle of a website; within that rectangle you could click through to browse the exhibition one artwork at a time. This entailed that your path through the Flash app was not connected to the browser's address bar and exhibits did not get a URL of their own. When you wanted to direct others to your piece the only way was by giving them a "Japanese visitor's address", as in "go to this well-known named point (the domain name), from there walk west and when you see a tall black building, turn right and take the third alley to your left, I'm living in the fifth house down that alley".
Nothing to replace it with to afaik.