Related to this, but building anything interactive in general was made super-easy by Flash because it was basically one IDE with everything you needed included out of the box. No complex toolchain, or ludicrous dependency tree, no nonsense build and deployment (though the fact that the default for Flash content was one giant binary blob wasn't always ideal when bandwidth was at a premium), no having to learn a new framework and toolchain every 12 - 24 months. And, frankly, were the security holes any worse than plenty of other apps at the time, or the constant parade of issues we see with our current dependencies that require ongoing vigilance and updates?

The big problem is it was proprietary and the cost of entry was high at a time when I was short of cash for quite a few years.

Still, I wish I'd invested in learning it back in the day, as I really only came to appreciate its benefits after its fate was effectively sealed by Steve Jobs: could have made some good money whilst having some good fun doing it for 8 or 10 years up to around 2010.

(Of course, I would have had to deal with the consequence of my skillset being obsoleted seemingly overnight, but I got kind of a taste of that from the Microsoft ecosystem as well: it's WinForms, no, it's WPF, no it's Silverlight, no, etc...)