We lost incredible capabilities when Adobe abandoned it and Apple signed its death warrant. Moreover, we lost the best authorship tool of its kind. Nothing has ever been as easy to use, easy to deploy, comprehensive in capability, and complete in functionality.
Adobe let Flash languish after the purchase of Macromedia.
Google hated Flash since they couldn't index it and use it for making money. Flash also competed with YouTube for eyeballs. (In fact, one of my favorite analogies for Flash is to imagine if YouTube was interactive - that was Flash.)
Apple hated Flash as it undermined their complete control over their device (no runtimes).
Microsoft hated Flash because of the security flaws and how deeply their browser integrated into the host OS.
Creators, however, used it to make the best experiences. If you discount the awful splash pages it enabled, the work being done in Flash was leagues above the web games you see today.
I wish Adobe had donated it all (editor and runtime) to the w3c as open source. We could have started to iteratively polish it into a standard.
Maybe WASM deployables will fill the gap.