Flash had its problems but as a user, it looked sharper and smoother than even current websites. And its editor gave non-tech users ability to create amazing animations, interfaces, and even games.
It could be smooth AF in ways that a video on a service like YouTube never could be.
I didn't get into flash games at all, but I used to watch Flash animations.
Like, for instance, Salad Fingers: https://archive.org/details/flash_salad-fingers
This was intended for a slow 2004-era computer with a 4x3 (probably 1024x768) display, where it worked very well.
But it's not 2004 anymore; things are much faster and screens have gotten a lot bigger. Here in 2026, Salad Fingers renders out fine at higher resolutions, and at different aspect ratios. It works great on my desktop at 1080p, without stretching [and with some probably-unintentional extra content on the sides]. It even works on my pocket supercomputer's 3200x1440 20:9 display.
Vectors are fun, and they scale as technology improves. The lines remain smooth and defined. And with Flash, that's a built-in: An unaltered 22-year-old digital animation still looks crisp.
For contrast, if Salad Fingers had been published on YouTube way back around that time, it would have been in chonky fixed-pixel 320x240. Maybe that would be as good as it would ever get unless it were rendered and uploaded at higher resolutions later.
Image-wise, SVGA + JS probably gets you the clarity. Standard gif / image animations not so much, if that's what you're referencing.
This isn't my baliwick, so I've absolutely nothing to say about the ease with which these options can be created.
wasn't some of that smoothness because it ran at a 100hz tick without any way of adapting it (and still running existing code)? That was the complaint I kept hearing from people attempting to make flash on phones viable (this led to ludicrous battery consumption)