Comment by GuB-42
Performance was way better than what we have now with modern web stacks, we just have more powerful computers.
I agree on security and bugs, but bugs can be fixed. It just shows neglect by Adobe, which was, I think, the real problem. I think that if Adobe seriously wanted to, it could have been a web standard.
Lots of people say performance was good, but that seems to be through the nostalgic lens of a handful of cool games.
Those did sometimes run really great, but most implementations were indeed very slow.
I remember vividly because it was part of my job back then to help with web performance and when we measured page speed and user interface responsiveness flash was almost always the worst.