Flash still seems more popular for webgame development. I've run across a handful of HTML5 games, but many more Flash games. Not entirely sure why. Libraries, maybe? Is there something comparable to Flixel for HTML5?

Createjs?

Or just write your own.

99% of all Webbased gaming is flash. Why? Because HTML5 is about at a point where flash was 5 years ago. Thats not just my opionion but facts (see all game portals, FB game etc.) and what the big guys say (http://www.wooga.com/press/releases/wooga-html5-project-goes...)

There are solutions in the works, but precisely timed audio (like games need) is still problematic in HTML5.

That is funny, but we haven't had that problem.

Using the html 5 video player sucks pretty bad in my experience (coursera).