Over the last 3 years, I have written written a few articles related to the readiness of HTML5. At this stage, I am confident that the only remaining leg-up that Flash has on HTML5/Javascript is a consistent experience across desktop environments thanks to the Flash runtime environment.
Technology wise, my team is now pushing Javascript / HTML5 futher than we ever could with Flash, which eases most of the anxiety we had originally when the market turned on Flash pre-maturely.
Check out some of the benchmark testing we were doing with maps and our new HTML5 library in CMaps Analytics