Being a GNU/Linux user myself, I also suffered all those crappy versions, late releases and crazy development cycles. But, looking back and trying to be fair, I must acknowledge that the availability of a Flash player for the major operating systems has lowered the barrier for multiplatform development for many people, specially for independent companies. And I'm not talking only about embedded videos on websites, but also videogames (like Machinarium or VVVVVV) and applications. In some sense, Flash was more successful than Java at building bridges between platforms.
That said, the failure of Flash on mobile platforms is not surprising at all. Pride seems to be the favorite sin for Adobe. They were barely able to produce decent quality versions for non-mobile platforms, so it was pretty clear their development work force wasn't strong enough to provide properly optimized versions for the more complex Android ecosystem.
Adobe rejected the option of freeing its Flash Player, while keeping Adobe Flash (the content creator) as a commercial product. Apparently, they feared publishing the source code of its player would make easier for its competitors to provide alternative editors. But competition is not a bad thing, as it usually enriches the ecosystem and increases the popularity of a product. And opening the player would have extended Flash to newer platforms, improved the quality of non-Windows versions, and reduced total development cost, giving them more chances to success on mobile platforms. Perhaps they would even won the favor of some other companies (namely Google), which would in turn embed support for Flash on their own products by themselves.
Adobe lost their big chance. Not even them understood the truly potential of their own product.