I played many great html games. Seldom of them can run/load successfully in all mainstream browsers. Some run/load failed in IE, some failed in FireFox, etc. And the differences of fps between different browsers are very large. In some browsers, a game may run smoothly, but in another, it is very laggy.

Flash still has the advantage on the consistency.

But how long Flash will still keep the advantage is really a problem for Adobe.