Audio support is a giant, basic problem. Games have sound.
Beyond that, all the code is in Javascript and out in the open, and the performance of Canvas isn't any better than Flash's software renderer.
You mention that hardware accelerated Canvas is going to arrive eventually in certain browsers, but hardware accelerated Flash has already shipped (as of last week). As well, Epic announced that Unreal Engine has been ported to the platform.
Beyond that, all the code is in Javascript and out in the open, and the performance of Canvas isn't any better than Flash's software renderer.
You mention that hardware accelerated Canvas is going to arrive eventually in certain browsers, but hardware accelerated Flash has already shipped (as of last week). As well, Epic announced that Unreal Engine has been ported to the platform.